Go above your supervisors head and report her to HQ. Tell her that your g.f wouldn't like that and walk AWAY from her if you can each time. Make a disgusted look like you find her repulsive.

Most people would feel rejected and humiliated at being rejected that way, lol. She so deserves if for being a creepy harasser. Can you get transferred to a different store or department? Just walk the other way when you see her. If she corners you, make an excuse that you have to help a customer or that you have to use the restroom. Go on your break right after she comes back from hers so that you're not around her as much. You work with a bunch of jerks.

Try my suggestions. Especially about the disgusted look and ask her if she's put on some weight lately and that insult should make her want to stay away from you probably, lol!