How do i get rid of my, "best friend"?

me and my friend kayla have been friends ever since we were little girls. but as we entered junior high and now entering high school, she just really ticks me off all the time. she never admits when she makes a mistake and whenever we get in a fight she always pins it down on me. even when we aren't fighting, she is always just really annoying. its not even like she is doing something specifically that's annoying, i just don't like her personality. she is very obnoxious. i was talking to my mom about it and she was even saying that kayla has been like this ever since she was a little girl. i don't enjoy hanging out with her and i've acted like I'm not interested in talking to her a lot lately. i know this sounds really harsh but I don't know what to do! 2 of the people in my "group" have stopped being her friend but i am the closest person to her so its not the same if i stop. she is negative and claims she is depressed and that is one of the reasons why i can't just blow her off like that. she even gets mad when i hang out with other people. plus, she is two-faced. and im not one of those people who will just agree with someone's opinions of another person, i say what i believe. i just can't take this anymore. please help me realize i don't want to be her friend anymore.