My girlfriend told police I hit her and she had a bruise that I did not cause.

This past Thursday my girlfriend and I got into an arguement, and I asked her to leave my home. She would not leave, I told her that I was calling my friend to come get me and picked up the house phone, and began to dial, she took the cradle from the wall and had thrown it at me and I dropped the house phone and went to my neighbors house to put some space between us. After being there for about half an hour I saw that there were police outside of my place and they were taking pictures of her. I walked over to them and they asked if I could write a statement. I had no idea she had called them. I wrote the statement and a few moments later was placed under arrest for cdv 3rd Degree. I asked what I had done and they said that she said I had struck her with an object of some sort. And that she had a bruise on the right side of her face. I did not strike her and she does have a history of self mutilation, can I be convicted even if her injury was self inflicted, she has no proof it was me.