Time outs don't work. And by that I mean the typical time out. You need to make the consequence of the action of hitting others far more uncomfortable than just behaving. I would personally have a play pen set up some where else in another room and EVERY time she hit someone I would swoop down on her give her a big old stern and very mean-faced 'we do NOT hit' and then put her in that playpen, close the door and walk away. Once she learns that hitting equals time alone and NO play time she will start to behave.

A child like this also needs to be stopped at every single inappropriate action. She is hitting because she does not trust that YOU are in charge and that YOU will meet her needs and the needs of the group exclusively. she needs to trust and learn that she is NEVER in the position of needing to problem solve herself by hitting etc. And the way you do that is to position yourself as the alpha dog.

Go here and read this:

http://www.justthebabysitter.com/201...lpha-dogs.html