Without this review (or the opening two paragraphs) I wouldn't have read this book:
This book was a ridiculous premise and winds up being pretty stupidly cute. It actually worked, where Isabelle could come across as a bit vapid or shallow when pitted against the guarded Millie, here she comes across as vulnerable, sweet and free-spirited--kind and loving too. She was delightful and slightly uncomplicated (though not 'simple'). Which made the novella just right for her. It's definitely quick, yet somehow convincing.
However, I suggest you just read Wollstonecrafthomegirl's review.