In my experience, the girl has always showered after the sex has finished, and before she tidies the room for the next punter. This would only be in my time if I finish a few minutes early, which is often the case.
I always shower in the main communal shower area beforehand, but leave my hair wet in the lounge so the girls know I've had one.
The girl having a shower before the event, on my time, I find unacceptable time wasting. Only ever had it at Blair Street.
If she showers after a punter has finished, she won't need another shower before the next punter.