My daughter's best friend has lice. since they are in constant contact, should i treat my daughter prior to a breakout?

Nit comb: A pre-emptive choice could be to use a nit comb instead. You can check your child weekly for nits. Treat only if you see nits, eggs or lice. Helpful website from the centers for disease control: http://www.Cdc.Gov/parasites/lice/head/treatment.Html.

No but inspect hair: No need to treat if lice or nits are not present on your child's scalp or in the hair. It may be worthwhile to buy a lice comb, very fine toothed, to comb and check your child's hair. Reinspect scalp and hair again in one week.