L.S.
I have a good idea of what you are going through. I have a 6 year old son and we just had our 2nd child in November. He likes being a big brother and he really seems to love his little brother a lot. Ever since I was pregnant my older son has been out of control. I know with a smaller child it is harder for them to understand a lot so it might be a little bit harder. What we do is a star chart. Every time my son does something good he gets a star and every time he does something bad he gets one taken away. At the end of the week he gets a quarter for each good star on the chart. For your little one that probably doesn't understand money, maybe it could be points to get something at the dollar store or maybe a treat that she doesn't get very often. Its something to make them stop and think about their actions. It seems to really be working for me. Also another thing to try is counting to 3. When 3 is reached and she is still doing what shes not supposed to, than take away the star. If she gets a negative amount of stars just remind her that shes got to work extra hard to earn them back. If that doesn't work there is always time out. You just have to make one spot the time out spot and every time they need to be put in that spot. Either way you must be consistant for it to work.
Thanks,
L. Scupien