You are not a monster. Both of you were innocent children.The fact that you feel sick about it ten years later is an indication that you may be a highly sensitive person. Sounds like she thought it was a game. Nothing more.

As Jennifer has said talking to another person is part of your own healing. Talking to a therapist gives us a way to get another perspective.

When I was 8 I was guilt ridden for years when I lied to my parents about an accident I had. I apologized to them and did tell them the truth but when I did do that she said that I had already told them what had happened. The guilt about that lie made me sick to my stomach.

Maybe there is something else going on inside your mind that is compounding this event. Please get help.