The hair dye fried all of them and I haven't had a problem since
I know for certain that works. I once had an older client - very fastidious - who would have died if I had told her while I was doing her hair that I saw a couple of lice on her. Fortunately I was applying haircolor and was pretty sure it would kill them. It did. Never saw a sign of them after the hair color.
I would never do that again. As a hairdresser, I am not allowed to work on anyone with lice. I have to stop working and ask them to leave the salon, no matter what state their hair is in when I find the lice.