Stalker Friend

A girl and I used to be friends. The thing about her: she seems stand-offish at first, then you get to know her and she's really nice, then you REALLY get to know her and she's creepy and moody.

When I was friends with her, i was always upset, stressed, and my grades dropped. After a while,I realized i couldn't stay friends with her.
I broke it off and she was mad for a while and then she got all "let's be friends again", to which I denied her.

Now, she's to the point of basically stalking me. She's in a lot of my classes, she switches groups to work in mine, she's joining all the clubs I'm in, and she's trying to get info from my friends and my mom.

I'm really creeped out, and she's making me really upset and stressed.

I don't need this. It's my junior year and I just want her to leave me alone so I can focus on getting through with good grades and hair on my head.

The school counselor SUCKS. (my friends and i talked to her last year about a boy being clingy to us, and she blamed us and didn't help at all. she blew us off every time.)

I've told the girl MULTIPLE times to leave me alone, both nicely and extremely bluntly. I don't know what to do anymore and it's causing me so much un-needed stress. :'(

PLEASE HELP ME.