She might not have accepted because she thinks you're going to try to friend her repeatedly. If she has an *** of a boyfriend, photos like that could create drama in their relationship. Its not to say that she doesn't fancy you, but to some, it isn't worth the added drama, esp. if one or both people in the relationship are insecure enough to allow photos to bother them. Btw, if you're making an attempt to pursue her, you shouldn't be anyway, shes taken. Just move on, if she comes around, cool, if not, that's cool too. Don't let her know you are pressed. That tends to push females away anyways.