God, can you imagine what her reaction would be if any of those old friends did as she claims she wants?
Marissa would demand to know why they're ending the friendship. She wouldn't be satisfied with this mushy, euphemistic, "growing apart" crap; she'd want reasons. And then she'd use those reasons to berate her now-former friends and tell them why they're the trashy, hateful, entitled losers, not her. Even if they didn't want to end the friendship, but felt they needed to do a true friend's duty by having a come-to-Jesus talk with her, she'd lash out at them, tell them why they were wrong, and make them the bad ones. Narcs gotta DARVO, man.
Because it's never her. She's never the problem. Nothing Marissa does can possibly be seen as so obnoxious or objectionable that quietly vanishing from a years-long friendship is justifiable. That her oldest friends are all ghosting on her is their failing, not hers. Or at least that's what Marissa believes.
I'm pretty sure her sexual acting-out (paid or not) provided the final nails in a bunch of coffins that have been years in the building. Sex is great, but the way she's going about it—multiple hookups each week with randos met on a dating app, boasting about it online, posting pics of allegedly post-coital urine-soaked puppy pads in her bed—would be enough to make me decide I was finally done with an obnoxious, attention-seeking friend, left over from my school or college days. Even if I was sure she was lying about it for attention and not having sex at all, I'd be done with her sickness. Sometimes, you realize that the situation is hopelessly unfixable and there is nothing to do but move on—and that's exactly what Marissa's old friends have been doing.