Have you explained to her your boyfriend problems, etc.? I imagine she's calling you so much because you're her primary relationship, and now that there's so much geographic distance between you now, she is very lonely. Please keep that in mind before you end your friendship with her. After all, when you first became friends, you must have thought she was a great person.
unfortunatly I have explained to her my situation and I do let her know that im tired and frustrated that I will give her a call when I feel better, but she dosnt give me the chance to. I dont want to be rude about it either, but its got to the point where I have to lie to her and tell her im going out of town so I can get rest but she still texts me and makes me feel miserable for not answering but I do have a life of my own. Today for example I was talking to my mother on the phone when I got a call from her It was important what my mother was telling me so I didnt answer I was going to call her soon, how I had agreed earlier today. no sooner had the call ended when she made another one I had 3 missed calls and 2 private calls and 3 voicemails I finally finished talking to my mother when guess what my house phone rang, I calmely explained to her that I was talking to my mother and for her not to be so desperate to which she replied "well your supposed to answer whenI call", I didnt reply anything and change the topic. everytime the phone rings our friends, my family, my boyfriend all jokingly always bet that its her.
You say that you're not in the mood to talk to her, but usually aren't your friends meant to be the ones there to cheer you up and help you work your problems out?
It sounds like you feel that she wants more of you then you would ask of her but maybe that's as much you problem as it is hers.
try to remember what made you become friends in the first place and try answering the phone first time, try to make the conversation as engaging and fulfilling as possible.
she'll probably feel the need to call less if she doesn't feel like shes loosing your friendship.