Was it my fault she got hurt?

When I was about 8 years old I had a friend that I hung out with that was about 15 years old. She asked me if I was allowed to walk with her and I said sure and then she asked me if she could come inside. I told her I can't since my dog would attack her and my parents will freak. She said common please and I still said no. Then when I was going to go inside she walked in and I just sighed and told her to wait by the door and don't move. When I came back my dog Petey came running and bit her on the ankle. Hard. She ran outside and went to her house. Her friend told me she had to get stiches. Was it my fault or hers?