Normal children do not bite. Since your child is biting, you must be a BAD PARENT. No doubt your child will soon be kicked out of Montessori school and grow up to be unhappy and friendless. She will be entirely correct when she blames you.Oddly, that is not what I have found so far.
The about.com page offers standard advice, most of which we have already implemented: be sure there are consequences, put the child in time out, lavish attention on the child that was bit and pull away from the biter, be sure that all caregivers (parents, daycare people, etc.) are on message. Another parent recommends this children's board book.
But all of these parents are dealing with children in the 12-18 month range. The Caroline Situation will be three in december. Why has my child started biting now? Part of the issue has to be the arrival of Tiny Joseph. Part of the solution, I think, needs to be letting her know she is still loved.
Should we establish a long term penalty for this? Should we say "no treats for a week" and whenever she asks for a treat, say she can't get one because she bit her friend? Does she have enough of a sense of time to understand this? Are we putting too much emphasis on negative reinforcement? Should we spend more time reinforcing her good behavior?