Does anyone have any advice on how to manage intense periods of rumination?

I am currently dealing with a very toxic co worker (micro managing, passive aggressive, refuses to work together, extremely hostile and mean in her approach). We are all at the same level in the team but she acts superior and tries to micromanage her colleagues.

My manager is fully aware that she’s a nightmare but she seems to struggle to deal with her (I feel for her as she’s got a baby at home and a husband in the military so she’s got a lot on her plate). I do go to my manager about certain things that I really can’t deal with, but even with my manager telling the bully to professionally back off, she then argues with our manager! I’ve also already been to HR and had formal mediation, which calmed her down for a bit but since she found out im leaving she’s increased the pressure - she sent me 19 messages or emails last week asking unnecessary questions, trying to manage my work, pressuring me or get me to do extra projects even though I’m leaving soon.

I have an end in sight as I work my notice period, but I find the autistic rumination so hard. I’m thinking about it over and over like my brain is trying to come up with a solution or figure it out, but that isn’t possible. I replay all our conversations in our head and it stresses me out more. Talking about it doesn’t really help either as I have done this in therapy and it makes me more wound up and the same with journalling. Any advice would be appreciated