Is it normal for my 18 month old to pinch herself?

She is pinching ao hard she is bruising herself. Shes also pinching me, daddy, and grandmas dog. She pinches grandma and grandpa too but not as much. We have been doing time outs so she has stopped pinching everyone else for the most part other than herself though. She does it when shes bored and when shes mad. Is it normal? Do i bring it up to her doctor? Last time i went to the doctors i had told them she was banging her head when mad and they said it was normal and not to be alarmed so i thought maybe this is normal and just another phase too?