J.M.
The most important thing at this age is to just be consistent. If she is pulling hair, a calm "NO!" consistently should do the trick. Eventually she'll get bored and stop.
At that age, they are still discovering - and trying to see WHAT gets a reaction out of mom. They don't get the concept of "When you pull my hair, it hurts, darn it!!!"
The other thing that worked for me was simply removing my child from the situation. If she is taking away toys from others at Playgroup, calmly tell her NO!, and if that doesn't work, just take her home.
Time outs didn't work for me at that age, as kids don't get that concept just yet.
Good luck!
PS If you think terrible two's is bad, wait till terrible threes! LOL :)