hmmm... when we introduced a very tiny kitten Allen to RB Sammy, she thought Allen was dinner. It took us weeks of introducing Allen to Sammy before we were able to leave them in the room without referees. They eventually bonded - when Sammy passed, Allen moped for the longest time for his buddy.

Could you try introducing and working with the two of them every night until they finally come to a peaceful co-existance?