Victoire Weasley and the Dream Stone (Book 2)

Victoire finished Hogwarts, and she and Teddy moved in together. They have a little cottage near her family and are very happy with their lives. One day Teddy goes into a store and buys Victoire a ring, but not your typical engagement ring. The ring has multi colored diamonds and is beautiful. Then things start getting scary. Everything Victoire wants comes true and everyone listens to everything she says. Her world becomes a completely different world than it was, and it's like a never ending nightmare. The only one who isn't trapped in this nightmarish world is her little sister Dominique. Dominique must help her get everyone out of this trance before it's to late and this becomes their world permanently. They have two months to save everything before they lose everyone they ever cared about.

You don't need to read the first book, Victoire Weasley and the Betrayal to understand what's going on, but I would suggest it.