I can't really improve on what anyone here has already said but I do want to add that in no way leave them alone together until much time has passed and you see that they're friends or that they'll at least tolerate each other. My RB Peeka hated my Pidge for years. Yours is just a kitten and can't really defend itself against a full grown cat. It sounds as though things will work out more quickly than you think, though, judging from your last post but you can never be too careful in this type of situation. Good luck and I do hope that things will calm down for you right away.