How can I get this girl to leave me alone?

I'll try to make this as short as possible. This girl who i used to be friends at started going out with this guy at our school who used to stalk me and be obsessed with me to a point where it was morbid. I lost all respect for her and completely disowned her. (it's a long story, message me if you want to hear the whole thing) I'm going to be hanging out with a bunch of people tomorrow and she's going to be there. No body wants her to go so she invited herself and i'm not the only person going to be there that doesn't like her. Basically she's annoying and gonna be following us telling us all her details with her boyfriend. I couldn't care less until she decides to give me weird looks likes she is PISSED at me. At first I decided to ignore it and wasn't going to go down to her level and give her a bitchy look back but once I accidently burst out laughing at her and I honestly couldn't help it cause she looked ridiculous. So then she decides to tell her boyfriend that I laughed at her and he attempted to cuss out not me but my friend who was with me because she has a facebook and I don't so he couldn't contact me but ANYWAY, I told his 'friend' that he should say that to my face and see if he could still walk after that and when he found out I told his 'friend' that, he freaked out and won't even step near me. (yes, he is a complete weakling) and now his girlfriend thinks I'm mean for threatening her boyfriend, which yes is kinda true. but anyway how do I get her to stop giving me strange looks?