3 years is a typical time for "independence". This includes the terrific with the not so terrific! Children tend to want to go potty by themselves, put shoes and coats on by themselves, pour their own drinks and climb the jungle gym. All the while yelling "watch me!" "look what I can do!", this wonderful age of independence also comes with the not so terrifics! They all boil down to CONTROL! All children like to be in control but once they hit the "independence" stage, their control is much more obnoxious and obvious. I am willing to bet, she has ALOT of control at home. Parents will often tell you one thing, but if you watch their behavior one-on-one with the child, you see a totally different story. Sounds like she is a typical "mouthy" and controling little three year old girl. You just need to take away her control. It is dif to explain exactly what to do, it mixes with saying the right things to the child and having the right frame of mind, you need to "exude control" with children or they will suck you dry!!!!!! Have a firm, matter of fact voice and look when she behaves unacceptable....you just look right at her and say "this is not the way you will behave right now" (i always find if you tell a child what they WILL do rather than say "please tell him your sorry" or "dont do that it's not nice" instead you look sternly into their eyes (at their level) and say "you will tell him your sorry!" or "you will not do that, it's not nice". She may just think she is running things, just let her know she's not.