You have to run them permanently to stop them getting in that state! All the pipework on hers will be full of algae and all sorts of other build up. We have had a hot tub for 15 years and always keep it clean and well maintained. You need to check the chemical balance daily and constantly adjust the ph and chlorine levels. Can't see her putting in that work, same with the pool. I bet she thinks she can just get it sorted and it will be good to go all summer ( we actually prefer using ours in winter to summer, much more cozy). You can't just leave it when not using it, the temperature of the water means all sorts of things will grow in it, including legionella if you are not careful ( the bacteria that causes legionnaires disease).