Questions: Girl's Behavior

So a girl from an online group started flirting and talking VERY sexual stuff with me intensely for (probably) no real reason about almost 5 months ago, and when I tried to warn her with a friend for a really toxic dude one month ago she instead got curious about him and is probably now talking to him almost every day and most likely doesn't believe me anymore. I think this because she kinda mocked me and my friend when I warned her a second time.

I contacted with her two times after that but it was rather not so deep and smooth as how it used to be. She replied in two minutes the first time and wasn't mean per se, just a bit vague and provocative. Apart from this, she used to say she even wanted to meet my parents and have my surname in 5 years, and talked about our family of millions of children about which I joked first.

All my friends are saying she's an attention-whore who never cared and just uses me and other men for her own self-esteem. Some said I could try to ask her to figure out about her true intentions from the beginning. Others said to just ignore her and maybe delete her everywhere.

What do you guys think? I'd appreciate your advises.

By the way: I used to have a crush on her but now I just distrust her. I'm about to end this shit in my head very soon. My choice would be either option 1 or 2, but I'm still thinking about it.

I can give you more details about the story if you want.