M.J.
So far I have had 2 kids go through the terrible 3's (it's not the 2's like they say it's the 3's). I remember having the "I am the boss" "No, I'm the boss" battle with both of them. 3's are hard as they are trying to assert their independence and they also don't know how to deal with all of their emotions. React to really bad behavior with a punishment and ignore attention seeking behavior.
Some things that help - 1. Try to get out of the house everyday, go to the park for an hour and let her run around. 2. Make sure she is going to bed early enough, my kids behavior was much worse when they were tired. 3. Be consistent, pick what you will follow through on and then do it. 4. Use a firm voice and look her in the eyes when telling her something is not ok. 5. And most importantly make sure you gets some, you time. Not just you time in the bathroom crying LOL.