I honestly wouldn't worry about the mildew on the wall. You just need to clean it up ASAP before it gets bad.
I have tenants that let mildew grow onto the walls in bathrooms, if unchecked it causes a problem. But any normal household cleaner should be able to get rid of it. It's what I have to do when they can't take care of themselves.
I don't know much about your living space, renting / owning / parents / etc, but there's also specific mildew resistant paints you can buy. This is the stuff that I use to paint all my basement rafters with to protect them from moist nasty basements.