Boundaries Kevin Boundaries, her mother gave in because it was easier to give her her way.

My 3 year old grandson, would throw a tatrum, whining crying etc. then his mother would give in to shut him up, after seeing this a time or two, I flipped on her! I told her that if she continued with this crap, it would only get worse! and when he became a teenager she would have hell to pay. He didn't display this behavior while in my care, or at school.
It is a learned behavior.