Are you serious because she doesn't want to use a car cover?
no car cover they will love that .. they try once to get on a slick car and fall off, they stop trying
Any luck with the slick hood?
Go with a good quality car cover and you won't be buffing out the claw marks. A lot of folks are anti car cover but I have a car that sits outside 24/7 and without a car cover I would be washing it every day. Keep it tied down and don't get one that has that placticky stuff on the outside.. Nothing short of tying a dog to the car will keep a cat off the car. They love the hood after you drive it for the warmth.
I was told there is no leash law but don't know for sure because I haven't looked into it.Is there a leash law in your city? If so, find out where the cats live and send a letter of complaint to the owners. If that doesn't resolve the situation, call the animal control dept. and they'll send someone out to speak to the owners. Animal lovers can be a PITA with their out-of-control pets. I do that with barking dogs all the time; luckily the owners around here are reasonable most of the time.