I agree, get a behaviorist. I would try to keep her in a secure pen.. if she can dig out, prevent that by either putting in some underground wire or putting her on a long line. When she's inside, put Sunny in a safe place. Gonzo used to be very intense with cats... I would not say agressive, but he'd stare them down for hours if we would let him. If a dog is allowed to chase cats, most will kill or hurt them if they can, that's just how a lot of large dogs are. Do not let her out in the open, with cats around. A lot of socialization and desensitizing could help her... but it's really strange that Pandy would kill a cat when she has been around cats in your house a lot, I think?? ^..^ anyway, she's beautiful, and I hope you can find a way to curb this.

The nipping, a dog should never be able to do. My border collie would love to herd and nip at cats, small animals, children, and cars, but he is just not allowed. When we got him he thought that was acceptable behavior--you just have to teach your dog that it isn't, and try to re-direct the herding behaviors. If she is nipping for territorial reasons, see a behaviorist about that.