i don't know about you, but i dont won't to read a book with french, sice i know about two words of it. I admit its sorta unlikely the english words ryhme (well, mostly impossible). Also, to be a poem it doesn't HAVE to ryhme. But I think this is a slip up, the author probaly didn't think about that.
so wait, you want her to write it in french, and then people who read the book to understand it? the whole purpose of writing it in English is so that the reader could understand what a good writer Anna was, and so that he/she could understand what it's about!