she is like that because she's insecure, to make herself feel more secure, she has to make you feel bad because if she can make you feel bad, she make herself feel better, people with low self-esteem are notorious for this, they have to put on that hard bitchy exterior to make people believe they're tough but they're not,
and she uses whatever tactics she's used in the past that worked on you but they don't work anymore do they ;-)
When she acts all bitchy towards you, just smile confidently and ask her with a grin, "is there anything else I can do for you today princess? I'm a busy man and don't have a lot of time for your crap behavior, if you can't be respectful towards me, I can't waste any of more of my VALUABLE time" and smile and then walk away.
Don't tolerate her crap behavior and for pete's sake, DON'T REWARD her crap behavior with her attention, when you stop paying attention to her when she's "bitchy" and you make a habit of not tolerating this crap, you will eventually send a clear message to her, you have respect for yourself, enough respect to let go of the people in your life that don't value you or the relationship they have with you.
It's called setting boundaries, you decide how you let people treat you. If you allow them to treat you poorly, I bet you that they will, if you respect yourself and stop allowing people to act like this toward you, eventually they'll get the msg and stop - trust me, it works, it may not be an overnight transformation but it works!
