OK, this sounds really gross (and truly, it is), but it's the only way I was able to get rid of it when 4 of my kids came down with it (and the only way I could afford to).
Get a jar of mayo and completely saturate the hair with it. Pile on top of her head, and wrap tightly with a grocery bag. (Secure with bobby pins or clothespins). Leave on the head at least one hour. Shampoo 3-4 times to remove the greasy mayo. Comb through hair with a lice comb.
If you use this method, you will need to repeat 3-4 times every three days, as it will not smother all of the nits. In the meantime, try to keep her hair slightly "dirty"... contrary to what people tend to think, lice only like clean hair... the products that are put in hair make it hard for nits to "get a grip" on the hair and stay put. Put gel or hairspray in her hair every morning, to keep it from being too clean.
Treat everything else in your house... anything washable needs to be washed at the highest heat setting and dried at the highest heat, as well. Anything that can't be washed needs to be tightly sealed in a plastic bag (trash bags work well) for at least 14 days.
Good luck! It's a tough thing to get rid of, but with proper treatment, it will eventually be gone.