What else are you doing to treat your home and her surroundings when she gets it?
You need to think long and hard about everything she comes into contact with. My boys kept getting it over and over. I had to become a detective and figure out for myself they were getting it at the kids hair cut chain I was taking them to. When I stopped taking them and started cutting their hair myself, they stopped getting it.
Lice don't jump. There has to be contact. They can only live for a couple days without being on a person. Think about your home and surroundings. Chat with the school nurse. Be a detective.
The only time my daughter got it a teacher at school had been selling bows and headbands and let the girls try them on. Oy. That one ticked me off.
Best of luck. This too shall pass.
This. My son kept getting it and bringing it home one year. As well as a few of his other little friends that played together only at home. The other mom's and I were at the end of our rope. Finally someone mentioned it to the other mom she should probably treat her son. It helped for awhile but eventually my son couldn't go to their house anymore. It just kept happening.
Lice is hard work! I second everyone's idea about using hairspray and a leaving condition if you can. My dd had long, thick, curly hair. Her brother had 3 cases in last than 2 months, but she only had it the first time. Picking her hair was the worst experience.
Good luck!
Kelly