Rear end accident, whos at fault?

I was in an accident and rear ended someone. My friend said shes at fault, but I always heard the rear ender is always at fault. This is what happened:
She was stopped at a yield sign waiting to merge onto the main road and I was behind her. She kept inching forward then braking, inching forward then braking when she could have gone several times. I looked behind me and no on coming traffic. She let off the brakes, I looked behind me once more and slowly accelerrated only to hit into her. I jumped out the car asking her why the hell she didn't go and her response was it was my fault. Who's at fault here?

I know you don't want to hear this, but it's your fault. Looking ahead of you is always the way to go. Sorry, but in most states you are to blame for an accident like this. Lawyers may disagree, but courts usually rule against the person that hit the other one.