Minor update: At the end of the little kids' practice today, I noticed the mom (from across the pool deck) and wanted to see what she did. I watched and she went over to wait for her son to get done, and then I noticed that she was talking with the head coach for a while. After that, she wandered over by the locker rooms and (yeah!) was yelling into the locker room through the vents/slats instead of going to the door. (This is what I've been doing for years.)
So it looks like things are good for now. I, of course, will still keep an eye on it. I also learned that our president, who I contacted originally with the coach, doesn't really do anything. There is someone else, who I've known for years, and she's in the process of assuming the role. I told her about the whole situation (this was right before I saw the coach talking to the mom) and being the mother of a 16 year old boy, she was appropriately horrified when she thought of the woman walking in on her son. She turned right around and was going to ask the pool staff to put up some signs. I told her that the coach said she would talk to the mom, and she said she'd check with her first before she pursued the signs.
Thanks for all of the good discussion and back up.