We have had lice in our family several times over the years. We have
 used the chemicals and then discovered that, if it's not a very bad case,
it is possible to wash the hair well with regular shampoo, leave the shampo
on the hair for a few minutes, wash twice and repeat this every day
for several days. This has to go hand in hand with  checking the
head carefully and pulling out as many nits and lice as you can.
  I don't know if there is research to support this but it works for us.
  The other thing is to be very good about washing all sheets, pillow cases
hats, etc in HOT water and drying with HOT air!
  Good luck.
   Naomi Bar-Yam