Thank you for bringing up this point; something was in my mind as I read the statement that Marianne would never do this. Of course, all sorts of women had children out of wedlock through the ages including the Regency. That's why this argument that Eliza owned blame in the first place is specious. Jane Austen never blames anyone other than Willoughby for the seduction. She makes Eliza weak in understanding but in the same manner in which she makes Marianne overdone in sensibility. Both are very young women who have to grow through their difficulties.
And I agree that the "Emma is at fault" discussion can't be resolved.