Again though, I think the "sisters" angle takes something away from Diana. She's got something of a fairytale childhood as it is, and I think it makes things more interesting to have her be able to say "of course I had a wonderful family... but I never had any children my own age to play with..." Having her get a companion by magic (and not just any companion, a companion magically guaranteed to be her perfect match) just makes her childhood too perfect for me.
And thanks for the correction on ambivalence. Was almost an English Major (it's what my grades and teachers said I should go for), but science lured me away...