I know what thats like as Miquelito can be a Bully Cat sometimes , and will chase Poucierge around grabbing her by the back of the neck. I wish I could tell you what to do about Lexie, but once a Cat gets something in thier mind, sometimes you cant get them to stop.
Especially when they MEEEEEEEEEEEEEEEEEEOOOW, I know what that can to your nerves!!!