B.H.
My boys are past this stage (they are now 11 and 7), but I know from raising complete opposite kids - some kids respond to NO and time-outs -- but some kids need to understand why they can't bite and hit.
At this age, perhaps role playing with her favorite doll would help. Get her favorite toy/doll/animal and have her pretend to talk for the doll and have another 'toy' hit her favorite doll and have her play out how that makes the doll feel. So you're putting her in the other side of the hitting, w/out actually hurting her.
Patience is a virtue at this stage -- take a deep breath and remember that this time will pass. Getting upset isn't going to fix the situation - it's only a stage. I try to remember the following: you can't change the situation, you can only change the way you react to the situation.
Good luck!