Edit: Stop seeing guy for sake of this girl?

What advice should I give my friend?

A dude came to work 2 months from Mexico, they met at a birthday party and instantly clicked, they started casually seeing each other and she made it clear she only wanted a FWB situation since she just got out of a SUPER long relationship.

He leaves to Mexico and she gets random messages from a girl, finally she agrees to talk and turns out she's a girl he messes with (according to him) but to her they were together but says she's breaking up with him after this.

Some time passes and she weirdly stays in touch with my friend. She's "single" according to her social media status, and the girl sometimes messages her but reiterates that she doesn't want anything to do with the guy so my friend continues texting with him.

He let her know he's coming for a couple of weeks for a wedding and wants to bring my friend as a date and basically just be around her this time and she agrees.

The girl messages her today and asks if she's gonna see him, friend asks why, girl tells her because she knows about her. My friend says they're not together so what's thr big deal. Girl says "Well, but we kind of talk sometimes, and I think I might want to work things out again".

My friend calls it bullshit, but still wants my opinion. She honestly doesn't care if he's casually dating because they're not exclusive and she doesn't see a future with him other than just seeing him when he comes to the state. Any thoughts?? EDIT: My friend didn't keep in communication with the girl. The girl started following her and would occasionally comment on her story, sometimes things about not letting guys win and stuff. That's how she knew they weren't actually together. She just didn't want to be a bitch to her since it seemed pretty harmless but she's blocked her now. The guy actually did mention this girl when they met, but said it was more of a loose friends with benefits situation.