What happened to Eliza Williams after Willoughby seduced and abandoned her? Joan Aiken's literary fan fiction answers that question. Eliza Williams grew up in Byblow Bottom, fostered by mercenary and neglectful Hannah Welcome and surrounded by illegitimate offspring allowed to run wild. Fosters also cared for legitimate children, particularly rich ones, until they were out of toddlerhood. Hannah Welcome's daughter fostered Therese Wexford, at least until she tried to sell the baby to a gypsy band. Eliza rescued the child and became the frail, developmentally delayed (the child had spent her first two years barely spoken to or touched) girl's companion.
When the Therese's father, the local squire, dies in a riding accident, Eliza contacts Colonel Brandon's attorney with the request to attend school. She never meets Brandon (he's rejoined the army and Marianne has left Delaford with him), but Eliza does stay briefly with poverty-stricken Elinor and Edward Ferrars before leaving for the Bath school their daughter Nell attends. Lodging with a barely respectable relative of Elinor's, Eliza prepares for life as a governess or music teacher (the best that an illegitimate girl with polydactyly can hope) and has begun her career at 17 when fighting off an attempted gang rape leads to her disgrace. From there she travels to London (staying in a millinery-brothel), comes under the protection of her late mother's last (and good-hearted) protector, and reunites with Therese an her mother in Portugal.
As a novel, Eliza's Daughter is entertaining if a bit too reliant on coincidence. As Austen fanfic, it's just wrong. Like The Private Diary of Mr. Darcy, the characters aren't consistent with Austen's. Colonel Brandon would not abandon Eliza to Byblow Bottom. She may have been Willoughby's daughter, but she was also the granddaughter of Brandon's first love. Eliza's life would have been like Harriet Smith's - sent to a respectable school where she'd hope to marry a respectable man, maybe even one of Mr. Gardiner's sons. I can't see Marianne as a bitter woman who'd punish Willoughby's daughter either, and even Fanny Price at her worst wasn't as priggish as Aiken's interpretation of Edward Ferrars. Overall, I found Eliza's Daughter compelling, but frustrating.