I was messing around and found this link:
http://www.mapertontrust.com/headlice/
Seems a bit 'different' and I have no idea if they ship overseas, but hey...if it works, and you have to keep facing the girls who are having a hard time of getting rid of them, it couldn't hurt!
My aunt also used tea tree oil in her shampoo after her daughter suffered from a very stubborn case at her school. She went through three VERY expensive treatments of her whole house before she started using it in her shampoo, and hasn't had a problem since. There's tons of info if you just search 'tea tree oil and lice'. As to how much to mix into a certain size of bottle. But I have to say, this was AFTER she washed EVERYTHING with bleach and/or the lice treatments made for the job. (the biggest reason it was so expensive was because she has two other girls, herself and her husband, and she had to treat them all the first two times).
I also think the hat is a good idea, also a leave in conditioner, or gel/hairspray and a ponytail couldn't hurt either!
Good luck!