K.P.
Check out the "When Dinosaurs..." series. They have one on divorce that's pretty good and appropriate for her age level. I would also suggest asking your local children's librarian for a recommendation. This is the person who could really point you in the right direction and you can check-out a couple of different options. If there's one that your daughter connects with, then you can buy it to have at the house!
**Counseling is a wonderful resource, but keep in mind that not every child whose parents divorce needs a therapist. Many come through it just fine as long as their parents are mature about the situation and put the child as the priority!**