S.G.
Yep-terrible 2's!!! And if you don't come up with a line of dissipline now, you'll have pretty much lost the battle later!! Now is a great time to start using the 3 count and time out. She screams because she is upset that you won't let her have the yogurt, that's 1. She hits you because you still say no (or better yet, ignore the screaming), that's 2. She screams or hits again, that's 3 now she gets to sit in time out for 2 mins and the time doesn't start till she is sitting there not throwing a fit. There is no arguing or hitting on your end at all. After enough times of this, you can put her straight into time out for hitting because she knows that is a no no. But telling her never to do that again isn't going to hit home with her at all. Stay firm, stay positive and stay consistant and you'll find yourself getting through this stage a lot easier than what you expected!! A great read (getting the DVD is an added bouns!!) is 1 2 3 magic. It talks about stop behaviours (hitting, screaming, whinning, etc) and start behaviours (cleaning up, going to bed, etc) and how to work with your child on them.
Good luck!!
S.