Hi Teresa.
Cat in your garden - cat is an intrusion - if the dog kills the cat no action will be taken.
Dog outside your garden - kills cat - dog out of control - dog receives a doggy ASBO with it's consequencies.
So don't muzzle your doggie in your garden Teresa if you know that the dog cannot exit the garden. This is your dog's safe play area. The dog is entitled to that.
Give her a big cuddle from us.