I would use the command *Leave It*, said in a rather stern voice when she starts barking at the cats. *Leave It* means don't mess with it, don't touch it, ....just leave it alone. You might also want to use it with NO. *No, Leave It*. Again, you tone of voice and a tug on the leash at the same time should convey that the cats are not to be bothered.
At PetSmart yesterday, they had one of the cats sitting in a cage on the floor as Hannah and I were walking through. Hannah came eye to eye with the cat and started barking. I immediately commanded *Leave It* and she knew exactly what I was talking about.
Other than that, I will have to let the people with dogs and cats chime in here.