M.E.
I have to strongly disagree with the below response from Karen. You dont teach a child not to hit by hitting them. She is suggesting that whatever the 2 yr old does to the baby, that you lower yourself to the 2 yr old mentality and perform the same abusive action to her. So if the 2 yr old pokes the baby in the eye, you should poke the 2 yr old in the eye? Does that sound even remotely intelligent? That is barbaric, and frankly the lazy way out. All you will do is make your daughter fear you. She looks to you for love and protection, not pain.
As far as easing the situation..you have to find out the cause. Something is causing this normally very well behaved little girl to act out. Most times when it is a younger sibling/child that they are acting out against it is because they feel replaced, or no longer the "baby" and the center of attention. Make sure your mom is spending adequate time giving your daughter POSITIVE attention when she is behaving. When things flare up, Dont waste time telling her to stop, get up, and remove her from the situation immediately, Diffuse it ASAP, and redirect her energy elsewhere until she has calmed herself down. I know that this can be physically demanding, but thats life with a 2 yr old sometimes, and you have to be diligent and consistent. Freaking out, screaming, yelling and God forbid, hitting her back is all negative attention that she will continue to provoke...because to her, then she is the center of the universe and you all are stopping everything to deal with her.
Protect the baby of course, that is #1....but do it as calm and swiftly as possible. The less hullabaloo the better. Dont reward her inappropriate behavior with a big to-do. I hope I am not in the minority here with my anti-hitting stance. I have raised 1 child to adulthood 2 to near adulthood and have another coming up...and have never hit them, ever. They are all well behaved respectfull people that know well how to use their brains and not fists to solve problems.