How do I stop being friends with this person?

[awesome person]

Well this person and I have known each other going on 3 years...
She's changed a lot, she doesn't care about things unless it's her way, like she called me one day to ask if I was going to her birthday party and I said no I couldn't because I was very sick and had a lot of AP homework, where she suddenly got an attitude and said "so?" and I was like "whatever" and then she just hung up on me. I thought friends were supposed to be caring? If one of my friends was sick I'd at least tell them that I hope they feel better soon and try to make them happy or something.
Also, this girl does not take anything serious. If you tell her something, she will blurt it out in front of everyone, and she's done this soooo many times at school. I've told her many things in my past that are bad, and she will act like she doesn't care.
I don't know. I don't want to keep being her friend anymore. How do I go about this? It will be hard because she's on my profile a lot on facebook and we have over 105 friends in common, so if I block or unfriend her she will find out. She's also one of those people who will text or call you many times just to make you mad. She also knows my parents facebook and also has my ex as one of her friends on facebook and I'm scared she will send stupid stuff to them or tell them things I've said or done.... Help?