Corps de l’article
Feminists point out that the social division of public and private realms is asymmetrical by gender —in structure, ideology, and practices—so that women's proper domain was the domestic, and men's was the marketplace. Ergo, women who took their plays into the marketplace transgressed gender norms, and to avoid damage to their sensibilities or reputations they frequently conducted their pecuniary, contractual, and dramaturgical activities by male proxy (a husband, father, brother, or helpful friend). But by accepting such an explanation, and normatively relegating women to the domestic realm, scholars replicate the oppressive ideology, for the domestic realm is a zone as much marked by male-defined ideology as the public realm; this is why the phrase "head of household" connotes a male, revealing how male authority and female subordination pervade all realms of the social, both at home and beyond.
Women had a great deal at stake in writing plays, for it represented in the composition, publication, reading, and performance, widespread and important modes of participating in the political act of sociability; as Jeff Weintraub puts it, this is politics in the form of "discussion, debate, deliberation, collective decision making, and action in concert" amounting to citizenship in the form of "participatory self-determination, deliberation, and conscious cooperation."  I argue that though it matters when women playwrights did successfully take their work into the public realm, it matters equally that many plied the craft within their homes or schools, because the "intimate domain of family, friendships, and the primary group" and the "instrumental domain of the market and formal institutions", which are in constant tension with each other, are merely a continuum of sociability (Weintraub 20-1). In this model, akin to what Bruce Robbins calls "a more relaxed, decentered pluralism (publicness as something spread liberally through many irreducibly different collectives),"  "the public" is not simply a place, a range of eligible activities, or even an idea; and it is certainly not the antithesis of "the private." Neither the public nor the private is bounded. Neither sphere is singular. One may garner more prestige at a major metropolitan theatre, registering strongly enough to enter the historical record, but activity in any realm was notable activity, and in many respects it was the same activity.
When Joanna Baillie writes to another woman about retiring to her study to prepare the last edition of her plays, she illustrates this issue beautifully:
I have been much occupied since last [J]une in correcting the proof sheets of my new publication. I thought I had done with all this business, but circumstances arose to make me desirous of leaving all my Dramas in print corrected under my own eye, so I was obliged to throw aside the indolence & desire of quiet & privacy so nature[al] to old aye [sic]. 
In other words, retiring into her study to correct proofs constituted a public act, for it would result in publicity, publicness, and posterity over which she exerted agency. The house-bound woman had many ways to be public. Jane Porter describes how, in theatricals put up by family and friends involving a new play by her sister Maria, an audience of twenty people made her fearful, yet the next night's crowd of fifty people "terrified to death all of us" because of their numbers and because they included individuals who were not part of the Porters' regular circle.  Thus, even within the home theatrical, varying degrees of exposure were incurred when audiences expanded beyond the close circles of everyday sociability. In this approach to women's dramatic and theatrical activity, we not only pull into focus the dynamics of the commercial stage as a domain of activity, we shape the public sphere rather than taking it as a given.  This "associative public sphere" is where socializing and cultural production occurred —be it a salon in which women predominated, or a men's club where women were banned—as distinct from the "solitary."  The public, in this formulation, aligns with the perceptible and thus the authoring of a play necessarily implicated publicity (publicness) whether it was bound for publication, home theatricals, professional production—or even utter obscurity.
Placing women thus in the public realm forces the question of how to regard women playwrights as "representative citizenry" when, in an official sense, they are neither representative of citizens (enfranchised men) nor fully authorized as citizens who make representations of things (such as artists). Are they representative of women sharing their class and background, of other playwrights, or perhaps of women in general through the characters they created? Do they achieve the status of the bourgeois citizen because they adopt sanitized modes of address,  passing censorship and eschewing what is recognizably radical? Is the genteel authoress more of a representative citizen in not publishing or professionally producing her plays? Or is her niche—as an adaptor and translator, or a children's dramatist, or an author of recital pieces in dialect—indicative of the "broad church" which we will write into the historiography of representative citizenry? Shall we let women succeed on their own terms?
Bernard Miége argues that whether a performance is "in an artisanal, a capitalist or a non-market form (amateurism)" it is all still within the capitalist relations of production.  These are useful reminders that "separate spheres" is not necessarily the optimal metaphor for understanding relations of a playwright to her environment (or posterity). Working in non-market (amateur) circumstances does not necessarily constitute marginalization. If they do not sell their work to commercial theatres, if they write with profit for only a reading, amateur, home, or school market, or even if they accrue no payment of any kind for their dramatic writing, they still exist in relation to others who do these things. They are not lesser, or necessarily even different, but are contiguous with others who pursue the same craft. Thinking otherwise would render Hannah More lesser than Elizabeth Inchbald, rather than focused in another direction with another purpose.
So, in conclusion, the question is not were there women, but where they were, and the consequences. The conventions of theatre history send us to look on the commercial stages, especially in London and specifically in the patent houses as the most aesthetically prestigious venues. While many women had plays produced in such venues, it takes more than mere presence to make a house (to borrow a proverb) a home, as many critics' reactions testify. In all likelihood, women's plays remained an oddity on the commercial stage for more reasons than just their numerical inferiority. We need to investigate women's lives and their work in a context for interpretation that sets theatrical activity within the options for sociability, construing this in Weintraub's terms: "discussion, debate, deliberation, collective decision making, and action in concert." My final example is from the other end of the nineteenth century, but it is still relevant. Florence Bell beautifully epitomises the point in her instructions for Fairy Tale Plays and How to Act Them (1899), addressed to children and their parents:
Some people prefer to make the auditorium quite dark during the performance. Personally, I find this depressing at an amateur play, which is a social occasion as much as a dramatic one. . . . The methods of Bayreuth or of the Lyceum, which I have heard invoked with great gravity in discussing this particular question, do not seem to me to bear upon it much. 
Playwrights, thus, operate within their own (appropriate) communities of speech and action.
The outcome of this varied amongst women: Jane Scott achieved local notoriety whilst Joanna Baillie came to national prominence; Baroness Elizabeth Craven wrote a dozen texts for private production whilst Fanny Kemble was produced by professionals across the nation; and Elizabeth Inchbald was an actress who wrote plays, whilst Lady Barbarina Dacre was a verse playwright who also engaged in translating. What is true across their ranks, however, is an economy of exchange instrumentally connected in multiply overlapped spheres. If they are classified as a counter-public sphere— as opposed to one integrated with but not necessarily visible to what is historicized as the public and private—it sets them aside, oppositionally and marginally, rather than as minor voices within the dominant culture and historiography. Because they are in no way unified, either mythically or actually, they are not a counter-public but rather part of the public sphere struggling with the structures and settings of sociability leading to representation.
Jeff Weintraub, "The Theory and Politics of the Public/Private Distinction," Public and Private in Thought and Practice: Perspectives on a Grand Dichotomy, ed. Jeff Weintraub and Krishan Kumar (Chicago and London: University of Chicago Press, 1997) pp. 11, 14; hereafter abbreviated as Weintraub.
Bruce Robbins, "Introduction: the Public as Phantom," The Phantom Public Sphere, ed. Bruce Robbins, (Minneapolis: University of Minnesota Press, 1993) p. xxi.
Joanna Baillie to "Anna", an unidentified correspondent, 12 December 1835, University of Glasgow Special Collections, MS Gen 542/7.
Diary of Jane Porter, 25 and 26 May 1801, Folger Shakespeare Library M.b.15.
Paolo Carpignano, Robin Andersen, Stanley Aronowitz, and William DiFazio, "Chatter in the Age of Electronic Reproduction: Talk Television and the 'Public Mind,'" The Phantom Public Sphere, ed. Bruce Robbins, (Minneapolis: University of Minnesota Press, 1993) p. 100.
Lawrence E. Klein, "Gender and the Public/Private Distinction in the Eighteenth Century: Some Questions about Evidence and Analytic Procedure," Eighteenth-Century Studies 2.1 (1995); Howard M. Wach, "Civil Society, Moral Identity, and the Liberal Public Sphere: Manchester and Boston, 1810-40," Social History 21.3 (1996); Seyla Benhabib, "The Pariah and her Shadow: Hannah Arendt's Biography of Rahel Vernhagen," Political Theory 23.1 (1995); Alan Wolf, "Public and Private in Theory and Practice: Some Implications of an Uncertain Boundary," in Weintraub and Kumar.
Melissa D. Deem, "From Bobbitt to SCUM: Re-memberment, Scatological Rhetorics, and Feminist Strategies in the Contemporary United States," PublicCulture 8 (1996): 527.
Bernard Miége, The Capitalization of Cultural Production (New York: International General, 1989) p. 25.
Mrs. Hugh [Florence] Bell, Fairy Tale Plays and How to Act Them, (London, New York, and Bombay: Longmans, Green and Co., 1899) p. xv.