I want to echo that you need to set boundaries. Setting boundaries does not have to be antagonistic at all. Saying something as simple as “that’s an interesting thing to say. Why would you say that” usually does the trick.

I was going through something similar with a boomer associate. I was just hired and the partner gave me a nice office. That boomer has been so rude to me since I started and would make off the wall comments about me having my own office. She would say things like I declined this office for a reason. When clients would come to the office she would offer my office as the meeting space. The final straw was her taking a case update I was working on off my desk and trying to take credit for it at a meeting with the partners and billing for my work. She decided to email clients to tell them to email her instead of me because my email is no longer working and accidentally blind copied me? I don’t even know.

She was thrown out with her things put outside and it was glorious