How to be diplomatic when telling an ex-friend to leave me alone?

She is in my form. Recently she moved into mine and my 2 closest friends form, since then we all became more distanced not only from her each other too. I dint want to just say go away and leave us alone but I don't want this to continue. She claims to have an ocd with licking her self which i no is a lie because it takes lots of treatment and hard work to deal with. She is attention seeking in doing this, me and my friends would forgive her but she doesnt even know what she has done wrong and she all called me fat (which i would consider myself as an ideal weight for my age) and all of us bi***es to our faces and to other people in our form a set of bas*****, she has never said sorry and is trying to sneak back into our friendship circle Plz help