That image is a reaction shot from you having sex with Sally in the mens locker room showers. They're basically hearing you through the walls. I think you need to have fully trained Debbie and then meet Sally there at the right time.
Technically there's a way to get into the girls locker room in the morning once Amy has gotten as far as you can. (Which is not fully trained, that isn't available yet.) But it never unlocks like you're really asking.