I'm not saying she's personally responsible for the factory conditions (if anything I'd blame Disney). I'm saying that it's virtually impossible to create a billion dollars of personal wealth without negative externalities somewhere along the line.
There are ~500mm Harry Potter books in print (all years, all languages). Author royalties are between 6 and 15 percent of the cover price. She would definitely have been wealthy, but not billionaire.
What's your actual "you've provided too much value to willing participants" amount? If she negotiated royalties of 20% she would have been a bad person? If she put her money in an index fund and it doubled every 10 years, she'd become immoral later?
And her books sold well enough before the movies and merch.