Just seeing this now.

Mandy and Tommy lived together almost 2 years before deciding that just the sight of one by the other resulted in a huge fight. Tufts of black hair and me hollering. Mandy have been "living" in a spare bedroom for over a year now. Initially I kept her door closed, maybe 2 months. Then, I started opening it during the day. Works for us - Many NEVER ventures out of that room, though she could. At night I keep the door closed so I can sleep.

What causes this? Not a clue.

Sure hope the vet can provide some ideas!