I am not a model but I've had the experience of being cyberstalked by someone for six years. He harassed my employers, my family members, my friends, and wherever I was on the internet he would follow me and try to make my life hell. The unfortunate fact of the matter is that there's not a lot that you can do once the stalker has found you. They can create burner accounts, and even if support got involved and IP banned him, he could use VPNs to get around that.
I am not sure how helpful law enforcement in her area is with issues like this, but one thing to do would be clearly tell him to stop contacting her and screenshot it. Then continue to take screenshots when he continues to contact her. Then provide this information to law enforcement and let them know he is cyberstalking and harassing her. I know fully well that law enforcement often shrugs and does nothing, but it's one possible thing she can do, and since the two of them were involved she would be able to provide them with his actual identity which might make it more actionable for them.
And I can tell you what I had to do to lose my cyberstalker, but I know full well that some of these steps won't be easy or feasible for her as her professional identity is online, but just for informative purposes:
- Disable or delete all accounts that used my real name or likeness
- Disable and delete all accounts that had been compromised that I knew he was aware of, or that used the same username as accounts he was aware of
- Create new accounts using fake names or using new usernames
- Never use the same name/username on two different websites, as once he's found you on one it makes it trivial for him to find you on others.
- Never post photos of my face online, or identifying information such as my real name
Like I said I know this is probably not useful for her as she is professionally connected to using her likeness and her current usernames, but maybe she could glean something from it. She has all of my sympathy, and I hope she can get away from this prick and get some peace.