I have elder scrolls oblivion game of the year edition and i asked this girl named avita vesnia to follow me and now she wont leev she wont die and she just follows me around what can i do

I don't recall that character specifically, but if she's a fan from the Arena, you should be able to tell her to leave you alone by talking to her. If she's part of a quest you're on, you'll have to finish the quest. Or, start a new game.