Dear J.,
I once contracted lice when I was in high School. At that time I was living in Puerto Rico, and the mama's and grandmamas kept telling me to wash my hear with dog shampoo. In those days I had my hair really long, covering my back and it was full and thick so it took two of the small bottles of dog shampoo to get my entire head covered. I then combed my hair with the shampoo still in it, and while I was combing my hair, the little critters were being pushed off my hair and into the sink. It was a nightmare, so horrible. But the next week to make sure It was completely gone, I then got a bottle of RID and combed my hair again and finally got rid of them.
You may want to try the dog shampoo. Also, you may want to try and pick her hair and try to get the little eggs out as much as you can before you shampoo. Pick them out, and squeesh them. When you pick an little egg out, place the egg on your thumb finger nail, and with the other thumb finger nail squeesh it... if you hear it pop, it was a live egg that eventually will have become an lice... I am telling you it is a nightmare. These little eggs are attached to the root of the hair, so sometimes the comb does not take them all out. Try really hard to get as much of these out as possible. Then shampoo, comb, and then rinse and put conditioner on because the doggie shampoo smells funny. Then the week to follow try the RID. And do the same thing, pick her hair, you should be getting the little eggs, but dead ones (the eggs won't pop if they are dead)... shampoo, comb, rinse, then condition, comb while the conditioner is on again if your little girl is not too tired.
Good luck. Let me know if this worked... it is a process and with a four year old I imagine will be very tiring.
A.