Hey pal.
Hope you are well. This is a weird one!!!!!
Could there be any chance of an ovarian remnant, would be a weird presentation of that, but might be worth considering?
Could consider running an AMH to check? If there is not an obvious cause, it would be all the ‘usual’ behavioural things:
https://icatcare.org/advice/aggression-between-cats/
I think the gabapentin sounds like a great idea.
Scott 🙂
