Modern Building Regulations require mechanical bathroom ventilation, I doubt if anyone could be made to fit it though, as it's not new work.
It would definitely be good practice though.
I think it's worth a shot at asking them to provide it.......... if only in the interests of protecting the property.
Easiest way would be in the ceiling directly over the shower. Then duct it out through the roof, or through the eaves (soffit board)
Otherwise straight through the wall to outside.