L.U.
Has everyones head been checked as well? It is most often that more information is needed to help ones family. Here are two web sites that you can share with your child's father and his family.
www.headlice.org
kidshealth.org/parent/infections/common/lice.html
Helping to promote positive communication with your child's father in order to insure the safety; wellness and help your child see that her parents are able to better cope and work together should be prioritized.
If your efforts are unresolved and the needs for your childs health are in question. Then, you have no choice to tell her father of limits/boundaries you need to take charge in lieu of your child.
I hope that with more knowledge, you both would be able to work together. Good luck, and I hope this information helps.