I don't believe you should adjust your rates whatsoever. As others have said, your client needs to also list their cats in case any emergencies should ever come up. Ultimately you would be held liable as well as Rover, but that distrust would be placed on you, I feel like that may even be in violation of Rover policy. And of course, you want to make sure you're being charged rightfully and fairly. In addition to safety, consider that Rover already takes a fee and it's HOLIDAY. I would offer a discount only if after adding the additional pets that you, personally want to offer a discount simply because you want to, not on their request. It's all about what you as their trusted sitter feel to be rightful considering the time and effort you spend to make sure their furry companions have an exceptional experience. I know it can feel a little awful to say no, but you've already made such a sacrifice by not even adding on their cats! I'm sure they will understand.

I say, if you can separate them without issue, do so. Introduce them slowly and reinforce the bond you have with your cat so the dog can understand. We have also had this issue come up. It is quickly resolved. If it's really bad I recommend you call Rover or spend a little money on a doggy gate.