I bought dsd a car when she was 17 which was sold a few years ago as she spends a lot of time in London where its cheaper and easier for her to use public transport. We then bought her this car last year as when she stays here in the middle of nowhere (no reliable public transport) its useful for her to have a car so we dont have to give her lifts everywhere and also so she can help driving my younger kids around sometimes, so although this car is also tecnically hers its for our benefit and to be used whens shes staying with us, we are paying the insurance etc and she isnt allowed to just sell it.
Once a month she goes and visits her mum for the weekend and takes the car, her mum doesnt drive so during this weekend uses dsd and the car to go places she normally wouldnt be able to get to so spends a lot of time in it which is fine but she smokes constantly and when the car is returned for it to be used by my kids as well it smells awful.
Would It be unreasonable for me to say her mum can't smoke in the car?