L.S.
I would question how an 11 yo got a piercing with out parental consent, which makes me wonder if she or a friend did it. In that case it could get infected. You have 2 ways to go here. The first is take it out, ground her, make her miserable by watching her every move. The second, sit down with her and tell her it's great that she is making grown up decisions about her body. Pretending to be grown is grand and she can continue with this like if she wants a cell phone she can get her own phone plan and pay for it, if she wants cable in her room she can pay for that also. If she wants to be grown and show off her new belly ring then she can be grown and only have what she can afford. See how long she last trying to be a grown up!