No way to know if a WL was actually busy for her entire shift. I doubt many girls, if any, would be booked out for the whole duration on 12+ hour shifts.
Then, she could also be taking breaks to eat/nap/bathroom.
Whether or not she is still enthusiastic late into her shift. Well, that depends on the individual WL and... maybe their impression of the customer. Lol, I imagine they could be judging their customers comparing to recent ones, especially on the same day when it's still fresh in their minds.