Hi L.,
My now 2 year 2 month old is a biter. My poor 3 year old has had to suffer though this ordeal, but what I realized was that she went into a biting frenzie (whether happy, mad or excited) when she was teething. Unfortunately, she was a late teether and what made it even worse was that her teeth were coming out all at the same time (in groups). Nonetheless, it started a very stressful and agonizing time, especially for my 3 year old son, who was constant victim of the biting. Once the teething stopped for a particular group of teeth, she would stop. But it started once again when the next set of teeth began to come out (all at the same time).
She understands that biting is wrong and she gets time outs when she does it. But during that time, it's like she can't help herself. At this time, she has 4 molars coming out at the same time so my son, neice and nephews are all on alert.
Also, when the time outs didn't work, I would bite her (not hard)but just so she knows that she can't bite. It would make her very upset, but it did make her think twice about it. When I saw she was getting ready to bite I grabbed her arm and pretended I was going to bite her and she quickly stopped and wouldn't bit for the rest of the day.