I'm pulling my hair out, or rather the girls

I HATE lice! It is the worse most annoying little bug ever. A week and a half ago I had to pick the girls up from school early because they both had lice. So we did the lice drill. Cleaned their heads with the special shampoo, combed their hair, vacuumed the carpets and furniture, sprayed the furniture with lice spray, bagged all the stuffed animals, and cleaned all the linens in hot water. We brought the girls back to school the next day and she checked them and said we were good to go no more live lice. She has been combing Kaitlyn's hair daily to help get rid of the nits and yesterday her hair was completely nit free. She was great. Then today she was itching so went down to the nurses office and again she was covered with live bugs. They checked Natalie too and I guess again she just has the nits, but they still said she has to go. I asked the nurse what am I supposed to do? Every time we get rid of this they get them right back. She said other nurses in the area have also been dealing with a lice problem and I guess they are worried that these lice are resistant to the shampoos. So they aren't sure what they are going to do. She gave me some more shampoo though and told me she would get them some plastic mattress covers and pillow covers to try to help us get rid of them. So they are missing another day of school and I'm frantically trying to do all the cleaning and comb out their hair all on my own today because Joe is at work and I have to work tonight. I am so ready to just shave their heads and get it over with. This is so crazy. I can't believe they have it again.