what is going on with my friend?

ok: my friend has really been confusing me lately as firstly she fancies 3 of her guy mates one after the other and then she insists shes not interested in boys and dating and just now she was talking to a teacher and as soon as he left she went into a fit of giggles.

so i was wondering what you thought- is she having problems with her sexuality or does she actually fancy the teacher (male) as she also went through a phase of trying undress another one of my friends who has now left the school (not because that though) undoing her bra and pulling down her skirt.

thanks in advance i'm really confused and don't know what to think or do.