When our children were younger, lice came home at least once a year from the "reading pillows" in the library at school. The "stuff" we used was NIX, but it contains permethrim, which was a problem for our daughter with asthma. Flash forward to the grandchildre - same issue, the lice come from both church & school where they are, & 3 of the 3 grandkids have asthma.
Sooo - - now that you have used the "stuff", be aware that you can also kill lice with an oil treatment to the hair. Olive oil works GREAT. You warm the oil, apply it, & wrap the head & hair in an old towel, "& have a beauty treatment", while you paint fingernails or toenails, or whatever. The warm oil both suffocates the live lice & removes the protective coating from the eggs(which kills them) & helps to loosen the glue holding them onto the hair shaft, but you still have to fine-comb. This is more easily done BEFORE you wash out the oil treatment. Then you shampoo & the hair looks like hair does after a warm oil pack - - great!
When our oldest g-daughter was about 10, she became very self-conscious of having lice, & so whenever anyone in the family came home with them, the boys got a buzz cut & the girl's had a "pamper party night". For the cost of a small bottle of nail-polish, DD turned lemons into lemonade.
You can also use the freezer to kill lice - - works better for things like hair elastics, etc. Just pop them in a baggie & into the freezer for a week.