SOLVED. fantasy/portal book about kids who enter a new world and visit a monastery and are fed food fertilized with human bones read around 2011-2013 [s]

[Morgan]

I am helping a friend who is looking for a book that she loved in middle school (around 2011-2013 time frame) I am not sure if this post contains spoilers as I haven't read it and she has. She remembers the book being older and thinks that the cover might have had children and a mirror on it or could have been yellow but she isn't sure. The book was about a group of kids/friends, both boys and girls, who travel to another world through a mirror/book. She remembers a point in the book where the children come upon a monastery and are taken in and fed. But they later discover that the food that they were fed there was fertilized with ground up human bones. She doesn't believe the book is very big/long. She thinks they are just trying to get back home from the other world but isn't sure if they had any special powers or abilities. In my search I asked her if it was Lord of the Flies, anything Magic Tree House, or The Mirror of her Dreams and she said it wasn't those. Any help you can provide is so greatly appreciated.

[Tab]

The Twilight Realm
They teleport through a mirror.
You can read the book on OpenLibrary.
https://openlibrary.org/books/OL26331...

[Morgan]

She said that was it thank you so much!