Mix peppermint oil with water and spray the hair daily. Lice don't like peppermint.
My DD had spent the night, slept in the same bed, shared a pillow and a brush with a girl who had a horrible lice infestation discovered two days later.
You can bet they were happily crawling around during the sleepover, but DD didn't get them....thank you, Jesus! I still itched for days, though. Lol.