How to tell someone you don't want to be friends anymore?

Ok, so there's this girl that goes to my school and her names Jasmine. At the beginning of the year at lunch time, I saw her sitting by herself and felt bad for her. So my friend and I went to go sit with her. She was really nice and funny at first. But then about a month went by and me and my friend regretted going up to her in the first place because we found out that the reason that no one was sitting with her was because SHE TALKS TOO MUCH!!!! So after a while, my friend and I decided to tell her that we don't want to be her friend anymore. So after school I sent her a text saying NICELY that we don't want to be friends with her. Now this has gone on for the WHOLE year! By now I've told her like atleast 4 times that we don't want to be her friend. Now first 2 times were nice, other 2 were mean cuz I wanted her to get it through her fricken head. The worst part....we sit RIGHT next to each other in PE and now Science as well. But I like one of her friends and her and Jasmine are good friends, so I thought if she can do it, then I could try to work with it. And boy was I wrong. Yesterday, she was OK, but today she just drove me crazy. We had to color a heart on a piece of paper and she kept asking what colors go where when the teachers example was right on the board. So I told her to look up there and she said, "I know but I just want to make sure I'm doing it right." If it's right in front of her and it's the teachers, I think it would be right, you know what I'm saying!? It's not exactly that, just she does that all the time and acts stupid and clueless. She's nice and all but just talks too much. Plus every single day she talks about her cousins since she lives with them. Trust me, she won't go even a day without talking about them. And in the past txts that I sent her, I've listed some of her issues, such as too much about cousins, too much talking, her saying watcha guys talking about too much when me and my friend are talking, and just that kind of stuff. Now most people that I know I would think they would try to change those issues but she just goes on with life as if nothing happened. Sorry if this is a lot but she just annoys the heck out of me. And in PE she chooses the locker right next to me everyday when there are so many others every where else. So how do I tell her to where it's not completely mean yet does progress in the end to where she doesn't talk to me again for like the 5th time? Plz plz plz plz plz plz plz plz plz plz plz plz plz help me. I'm gonna die if this doesn't stop!