Hi Jannie,
I just had to reply to this because I am going through a similiar situation. I ended a friendship a few years ago with someone I have known since we were children. I will probably make my own post about the situation, so that I do not hijack your thread

, but I just wanted to tell you that if you really don't want anything to do with her, just stop the communication altogether, or keep things very short as far as if you run into her or if she calls you, and continue to let her know how busy you are.
Of course the ideal situation would be to be direct and honest and tell her exactly what you told us. The thing is, how would she take it? If you word things in a way that doesn't make it seem like you are putting the blame on her, such as telling her that you feel you have both grown in different directions and you feel it's time to move on, maybe she will be angry or upset, but at least it will make things clear. And don't feel guilty, she will be fine. I'm sure she will find someone else to hang out with eventually.
I wish you luck with this. I think life is too precious to waste time with those who have negative impacts on us. You deserve to feel good all the time, and if it means letting this person go, then do just that, and move on.
Sujin