Wow lol, what a bitch. Tell her straight out, especially that she knows your dating your current GF.
On a side note, there is a fatass that likes me, and she loving looks like an ogre. In order for her to gain my attention, she loving walks behinds me and steps on the heels of my shoes making them come off. Not only is that annoying as forget, it's ruining my new shoes, and last week I told her off and said I don't like her, and infact I hate her. She never said a word to me again.
So tell her off, it works.