Headbanging

My daughter rocks back and forth in her crib so hard and hits her head, it rocks the trailer, she has two red bumps on the back of her head, doctor says we can't do anything besides keep and eye on it, and we are going to get her checked for autism, (she shows signs and it runs in the family, I have it) I'm just so worried, there's a smaller bump on one of the big bumps, it's so red you can see it through her hair. I can't put anything around the crib as she could pull it down and suffocate, does anyone know what I could do?