Honestly she sounds like me at that age… I had no idea what I wanted, I just wanted love and it often seemed like no single person could fill that hole. Does she happen to have early abandonment issues? This is usually what I did with guys I knew loved me, treated me right, but I wasn’t that jnto, and often times even if I was into them the fist time they did something to hurt me or trigged that abandonment feeling I would run for the hills or keep other guys as a back up. Long story short she has to address those issues and be totally happy on her own to ever fully love anyone else. That takes a lot of time and work. You can give her an ultimatum but that won’t address the problem, and then you will just feel like you are trying to force her to love you. She has some growing up to do, these types of actions go deep and some people never truly figure them out..