How to tell someone how yucky their bathroom was....

[Brandi]

Soooo my husband and I got this sand sculpture job out at this air force base called Vandenburg this past week. Really neat job. Saw where some major rockets of our time have been launched from. And got to go where no civies have ever been. But it was going to be a 120 mile round trip from our house.
So we have some friends who live close to the base so we called them up and asked if we could stay a few nights. They would never know we were there.My friend has been so happy to have a guest bedroom since her kids have finally left the house.
Well one night we got back to their place and they had made us dinner. It was so nice then we all went in the hot tub. Since we had worked a 13 hour day it wasn't long that my hubby and I were ready to say good night. But before hand we both wanted to rinse off in the shower. I naturally went first. OMG!!!!! There was black mold all over! The shower head was solid black mold!! all the grout was solid black mold. It was soooooo gross. And weird.
This friend is so clean (I thought) but this shower......and she had just had guest the weekend before. Her dad stayed with them over the winter (he is from Detroit and elderly). 2 of her kids are living back home right now too. All these people have or use this shower. WTH?
I am trying to think of a way to tell my friend without sounding like I am trying to tell her she is a not paying attention . And why aren't these grown kids cleaning this? All you would need is spray bleach and that would be enough. How to tell her?
After all they let us stay with them. Made us dinner. sigh! But someone else will see this.I need to save them!