If you are constantly separating your dog from the cat, you will never achieve a good balance.
I would strongly suggest that you put your cat in her carry case on the settee with Harvey placed calmly at your other side. It is imperative that you create a calm atmosphere when doing this, to stop Harvey getting out of control.
You may have to repeat this regularly, before your dog accepts being near Candy and vice versa, but once this is achieved you can bring Candy out of her carry case, restraining her gently and giving her gentle strokes in Harveys presence. With patience, they should both start to tolerate each other, and may even become friends.
Good luck.
