What book has a character named Neige and is about mirrors?

You're likely thinking of "The Mirror Thief" by Libba Bray. The main character is Neige, a young woman with the power to see into the past through mirrors.

This book is a young adult fantasy novel with a lot of magical elements, and mirrors play a crucial role in the story.

Let me know if you have any other details about the book you're looking for, and I can try to help you find it!