We just went through this with Riley - seemed like when he was around 15 months old or so he became a different child who had discovered his own will and boy did he exercise it! I think everyone goes through this but the key to getting your good little girl back is to be firm with the rules now, even if it seems repetitive (it will be) and gets tough (it will be). You are the parent and you have to win every time. Once she realizes this, you will start to see the little girl you remember again. It took us several months of "battling" with Riley and now I see my sweet little boy quite often

although I'm sure we will go through another difficult phase like that again and again and again.... Keep at it because this is the crucial time - if you don't stay firm now it will only get harder and harder as she gets older and then you might as well forget about it lol.