If it makes you feel any better OP, most lice prefer to infest clean hair. Although it would have been embarrassing for your friend to give you a heads up on the lice situation (no pun intended but whatev..) she should have told you anyway. Unless she was treating the problem and thought she shouldn't bother, which means she should have bought a new brush... This is your friends fault for not telling you, and your fault for sharing personal items. I guess you need to be warned not to use peoples chap stick/lip stick/lip gloss too..