First, understand that lice are resilient little bugs and can jump from one person to another very easily. This means that your daughter may be getting reinfested from kids at school, friends coming to the house, you, or other people she may come around (if she has it, someone else in the house probably does too). Also, tell the school so they can alert the parents- I have never heard of a school identifying the child who had lice, it's just wrong not to.
One effective way of getting rid of the bugs besides the shampoo (it seems like you have used this a lot and since the chemicals are strong it may start to dry out her scalp) is using the "smothering" method- lice, like all living things, need oxygen to survive. You can douse her hair in olive oil (I believe that thyme or rosemary oil also kills lice (one is a natural pesticide) so you can add it in with the oil) and wrap it in plastic wrap (securely) and then wrap her head with a towel. Keep her head wrapped over night and in the morning use the tiny little comb that comes with the shampoo and section her hair bit by bit and comb each small section out (I'd repeat this nightly until you seen no lice for at least a week- this won't hurt her hair at all). Also, lice HATE hair product so maybe you could make this all a bit more bearable for her by letting her use mommy's hair spray or mouse before school.
The worst part is that you need to clean house. I'm talking every surface she came in contact with. carpets, sheets, cushions- EVERYTHING!
If you're not diligent with lice and attack from all sides, you may as well just get used to having them around =(