C.M.
The only advice I have is to make sure you give her possitive feed back, more then negative. She is trying to get attention and if you give her the wrong kind she will think that is the one she wants. So if she does something naughty then give her time out but don't make a big deal out of it, if she helps with her baby sister praise her and tell her what a big girl she is and how happy that makes mommy. When she calls you stupid try telling her that it hurts your feelings and makes you sad, and see if that helps.
I hope this helps you, good luck I have a five year old and a 19 month old and a 4 month old...but they are boys