What is wrong with her? easy question?

this girl that I am dating refuses to believe that I truly love her and that I am not like the other guys that broke her heart. I have tried everything to convience her, everytime she gets ij detention I take it for her because I am trying to do something. nice for her. I took her out to dinner last night and she started making. a scene yelling at me and I asked her nicly. if we could talk outside because peiple were starting to stare but she yells louder. so I grabed her and took her outside she keeps yelling so I just told her to forget it because I was tierd of trying to get her to relize that I was trying to make her life better and I walked away. she grabed me and tokd me not to walk away from her but I did. what can I do I don't want to give up on her but she is being really difficult.