Let´s face it-women can be brutal to one another but there are usually three main reasons for bitchiness.
1. You did something to deserve it,and if so,that´s your own fault,so deal with it.
2. She is jealous of you
3. Sie is insecure and only feels better when making others feel like shit
Usually it´s no. 2 or 3 and if you´re an empathetic person ,you might actually feel sad for her deep level of self-hate :-P But I screw that! It´s time to put the....in her place. At this point there is no need to waste anymore mental energy on figuring her out.