First, stop criticizing yourself for how you feel!
I can relate to what you have described. I've worked with at least one person like that. I did find that once we were settled in in workplace, where it was just the two of us, she settled down and stopped acting as if she had to make a big splash all the time, which let me get to know the real person. My pet theory was that she was overcompensating for something with her public persona.
Anyhoo, practice focusing on her positive qualities, don't get into a negative cycle of thought. Try relating to her on a one to one basis to see if you can get along with her, rather than her behavior. Also, watch and learn from what she does that has a postive impact, and figure out if what she gets from it is a real rapport, or just surface level. I find that this sort of analysis can sometimes help me get past my negative reactions.
Is her taking your role over something imposed by management or because she will push you out? If it is management, guard against blaming her. If it is the second, use your words and be tactfully assertive to not get bulled out of the way.
I hope this does not sound sanctimonious. It can be really hard to deal with this sort of thing, I know.