|Maria Edgeworth by John Downman, 1807|
"I have made up my mind to like no Novels, really, but Miss Edgeworth's, Yours, and my own.—"The narrator of Austen's Northanger Abbey famously praises Maria Edgeworth's Belinda (along with Fanny Burney's Cecilia and Camilla) as a work "in which the greatest powers of the mind are displayed, in which the most thorough knowledge of human nature, the happiest delineation of its varieties, the liveliest effusions of wit and humour, are conveyed to the world in the best chosen language." 
—Jane Austen writing to her niece Anna Austen, Sept. 28, 1814 
Austen was far from Maria Edgeworth's only admirer. Belinda, published in 1801, quickly went through two editions and was later selected for inclusion in Anna Barbauld's series The British Novelists (1810).
But Barbauld also included a generous representation of women writers: Charlotte Lennox (The Female Quixote), Frances Brooke (The History of Lady Julia), Clara Reeve (The Old English Baron), Fanny Burney (Evelina and Cecilia), Charlotte Smith (The Old Manor House), Anne Radcliffe (Romance of the Forest and Mysteries of Udolpho), Elizabeth Inchbald (A Simple Story and Nature and Art), and Edgeworth (Belinda and The Modern Griselda). (That over the next few decades of the 19th century all of these novelists were eliminated from the canon is the subject of another post.)
A funny thing happened on the way to Belinda's inclusion in The British Novelists: the novel that was canonized was a different work from the one that was first published. Barbauld was something of a political dissenter, and in her view significant novels engaged with "systems of philosophy or politics" and had "some serious end...in view."  This idea of the function of the novel may be, aside from Belinda's popularity and Barbauld's friendship with Edgeworth, what recommended it for inclusion in The British Novelists. But the revisions Edgeworth made to the novel in preparation for the new edition removed or toned down some of its most politically progressive elements.
In its earliest editions, Belinda treats questions of gender, race and colonialism with a surprising freedom. The eponymous heroine feels "esteem" and "admiration" for, and finally becomes engaged to, the "remarkably handsome" Mr. Vincent, a "Creole" from the British West Indies with a "manly, sunburnt complexion."  Kathryn Kirkpatrick's notes for the Oxford World's Classics edition of Belinda suggest that in the early 19th century "creole" did not necessarily mean someone of mixed-race parentage, but rather someone born and raised in the West Indies (whether of European or African descent). However, Mr. Vincent's racial status, like his "sunburnt complexion," is ambiguous.
Ultimately Belinda breaks her engagement with Mr. Vincent, but not because of his race. Instead, it is because he is a passionate gambler, a vice she feels can never be fully overcome. But even so, Belinda and Mr. Vincent's lengthy flirtation with the possibility of interracial marriage is remarkable.
More remarkable still is the courtship and marriage between two other characters, Lucy and Juba. Lucy, described as "a pretty-looking girl of about eighteen," is the granddaughter of a tenant of Lady Anne Percival, the novel's epitome of good sense and felicity.  Juba is the African-descended West Indian manservant of Mr. Vincent.
In some ways Juba is a stereotypical character—he speaks in dialect, refers to Mr. Vincent as "massa," is superstitious, and plays the tambourine and "banjore." But he's also described by Lucy's grandmother as "a most industrious, ingenious, good-natured youth." The grandmother tells Lucy, with Lady Anne's warm approval, that "the eyes are used to a face after a time, and then it's nothing...make a prudent choice, that you won't never have cause to repent of."  Lucy makes the prudent choice of Juba, and later in the novel they celebrate their marriage.
But when Belinda was chosen for inclusion in Barbauld's series, Edgeworth (apparently under pressure) radically revised the story to remove any hint of interracial romantic relationships. In the 1810 and subsequent editions, Lucy marries an Englishman named James Jackson, not Juba (although Juba remains a character in the book), and Belinda only becomes friends with, and is never engaged to, Mr. Vincent. Incidentally, it is the revised 1810 version of the novel that is available on the Open Library and Project Gutenberg free e-book sites.
Who applied the pressure on Edgeworth to remove from Belinda the romances between English women and West Indian men? A letter Edgeworth wrote to her aunt Margaret Ruxton on 9 January 1810 suggests that the pressure came from Edgeworth's father: "...Juba the black servant is not allowed to marry the country girl Lucy; because my father has great delicacies and scruples of conscience about encouraging such marriages." 
Another curious aspect of Edgeworth's novel is that it features multiple scenes of cross-dressing: another kind of crossing of boundaries, this time of gender. Harriet Freke (pronounced "freak," meaning idiosyncrasy), frequently dresses (and even more shocking in the context of the novel, behaves) as a man. At one point she jumps into her friend Lady Delacour's carriage while en travesti, and when she is challenged by Lady Delacour's male companion cries out, "'Who am I? only a Freke!'" 
But Mrs. Freke, though the most prominent, is far from the only cross-dresser in the novel. Lady Delacour and her enemy Mrs. Luttridge dress as men to fight a duel, a masculine privilege. And early on in the novel its hero, Clarence Hervey, tries to win a bet with Lady Delacour by putting on a hoop skirt and being introduced to her company as "Madame de Pomenars."  (Perhaps Edgeworth is suggesting that the ideal man combines the masculine virtues of courage, confidence, and "animal spirits" with the feminine ones of delicacy and sentiment.) The cross-dressing episodes survived the substantial revisions for the 1810 edition; apparently the transgression of gender boundaries was less alarming than racial ones.
So Belinda, although it espouses traditional strictures on women's behavior and demeanor, is also strikingly modern—and perhaps it was this modern, critical view of the society in which its characters must find their way that was part of its appeal to Jane Austen.
After its approving attitude towards interracial romance and its more equivocal stance towards cross-dressing and gender ambiguity, a third modern aspect of Belinda is its self-reflexiveness. Several of Edgeworth's fictional characters compare themselves to characters in fiction, as when Mr. Percival observes that "husbands may sometimes have delicate feelings as well as their wives, though they are seldom allowed to have any by these unjust novel writers."  Clarence Hervey's first love, whom he names Virginia after the heroine in a romance, is "spoiled by early novel-reading."  And the book concludes in Chapter XXXI, entitled "The Denouement," with an arresting metafictional conceit:
'And now, my good friends,' continued Lady Delacour, 'shall I finish the novel for you?'----
'If your ladyship pleases; nobody can do it better,' said Clarence Hervey.
'But I hope you will remember, dear Lady Delacour,' said Belinda, 'that there is nothing in which novelists are so apt to err as in hurrying things toward the conclusion: in not allowing time enough for that change of feeling, which change of situation cannot instantly produce.'
'That's right, my dear Belinda; true to your principles to the last gasp. Fear nothing—you shall have time enough to become accustomed to Clarence. Would you choose that I should draw out the story to five volumes more? With your advice and assistance, I can with the greatest ease, my dear. A declaration of love, you know, is only the beginning of things; there may be blushes, and sighs, and doubts, and fears, and misunderstandings, and jealousies without end or common sense, to fill up the necessary space, and to gain the necessary time; but if I might conclude the business in two lines, I should say,
"Ye gods, annihilate both space and time,And make four lovers happy."'
1. Jane Austen's letters to her sister Cassandra and others. R.W. Chapman, ed. London: Oxford University Press, 1932, Letter 101, p. 405.
2. Jane Austen, Northanger Abbey, Ch. V
3. Claudia Johnson, "Let me make the novels of a country": Barbauld's The British Novelists (1810/1820). Novel, Spring 2001, 34(2): 163-179, p. 166.
4. Quoted in Johnson, p. 168.
5. Quoted in Johnson, p. 172.
6. Maria Edgeworth, Belinda, Chapter XVI.
7. Belinda, Chapter XVIII.
8. Belinda, Chapter XVIII.
9. Quoted in "A Note on the Text," Kathryn Kirkpatrick, ed., in Maria Edgeworth, Belinda, Oxford World's Classics, 1994, p. xxvii.
10. Belinda, Chapter III.
11. Belinda, Chapter V.
12. Belinda, Chapter XIX.
13. Belinda, Chapter XXVII.