The main cause of conjunctivitus is bacterial infection that infects the thin film of tears that cover the eye. I suffered with this a few years ago and my doctor told me it is very easily passed on (i.e. your daughter touches her eye then touches your hand and you touch your eye) apparently it really is that easily passed on!
Conjunctivitis (aka Pink Eye) is highly contagious. It's important that patients use separate face cloths and towels from the rest of the family. They should also be extra careful about washing their hands, especially after touching their face.