Well yeah you're correct. She's just craving for attention and being petty for it. Don't give her any reaction if she's does laugh again or makes faces of does anything absurd. As soon as she realizes that you don't care anymore, she should stop. Don't answer hers or her friend's messages anymore and if you see her friend again, and she tries to bring up the exgf life's details, you should tell her that you aren't interested in listening anymore. That should suffice. Act as if you don't know her when she laughs at you in public. Making fun of others at bus stations etc or any public place is rude and disrespectful. Especially when you did nothing to provoke such tacky behaviour. Don't lose your peace over this immature girl op. Good luck to ya. Hope she stops bothering you soon.