HELP! My husband's grandma bit my baby!?

My grandmother (my husband's mom) came over for a visit today. While my husband was in the kitchen getting some food for our baby and I was at the washroom, I heard my baby cry out in pain! I rush out into the living room with my pants still around my ankles and saw her biting my baby. When she saw me she stopped and then my husband came in. I told him what I saw but then he got mad at me because he really cares about his grandmother. My baby is bleeding and I don't know what to do with his grandmother. I punched her in the face and now I have a bruise on my hand. She isn't moving but that doesn't matter for now. My husband thinks a hobo did it so whatever. But please, how do I get this darn bruise off my hand? Also, should I try to sew my babies stitches up? I don't want to go to the hospital in case they see my bruise and force me into surgery to remove it.