I have a 21 month old dcg that is easy going most of the time, but has a history of pinching, hitting and head butting when she doesn't get what she wants. My 23 month old daughter gets the brunt of it since they are almost the same age and all the other kids are much older. But this morning for the first time the dcg bit my daughter on the arm, so hard that it almost broke the skin.

so any advice, other than a firm "no biting" and giving the other child lots of cuddles?

This dcg will usually not have any real reaction when I scold her (firm voice, not yelling). When I tell her no hitting, no biting she usually just smiles at me and says "Hi!" in an innocent voice.