Oh the tween years. For some reason they get a pretty bad rap, but have one daughter exiting this stage, and one in it, I have to saw tween girls can be pretty great! The hallmarks of the tween years is having one foot still in childhood, and the other in the teen years. This can make finding good devotion materials both difficult, and really important. Give your tween a devotion book she perceives as "little girl" and you've lost her, yet give her a devotion book written for teenagers and she might be thrown into themes about sexuality, drugs, and alcohol that she is just not ready to handle.
Our family loves Elizabeth George's Girl After God's Own Heart. I first discovered this book when my oldest was entering fifth grade. I was looking for a book to do as part of a mother-daughter bible study that I was hosting that summer. This book was recommended by another mom, and it was the perfect fit. The ten chapters in this book cover topics such as school, family, friends, and church. In each chapters girls look up verses and answer questions. It is a great bridge between little girl devotions, and more difficult and time consuming teen and adult bible studies. I would recommend this book for girls who are 8 to 12 years old.
The book provides small spaces to answer questions. Your daughter may appreciate having a journal to write her answers in to give her more space. Jim George has written a companion book for boys - A Boy after God's Own Heart: Your Awesome Adventure with Jesus.