IANAP but I talked to a sex-workers representative about this approx 4 years ago. (No, I don’t want to explain why!). She said they used diaphragms (effectively as Keepers, which were not readily available here at the time), which they would remove, clean and reinsert a couple of time each shift.
So, unless we have some Pros on the Board who are willing to chime in, this may be as near as we will get.
In the 1986 film Working Girls one of the prostitues is shown trying to insert a diaphragm during her period. Her friend comes into the bathroom and asks if the customer has injured her. Of course, this is from a work of fiction . . .
Here is a real life anecdote from my misspent youth:
I once visited an in-call escort. She was probably around 19, and there was another woman around the same age hiding in the bathroom (apparently, I wasn’t supposed to know about her). Anyway, I discovered that she had some wadded up facial tissue in her vagina. Soon after that she excused herself for a conference with the other woman in the bathroom. When she returned, she explained that she was menstuating and could not have intercourse. So that is what one prostitue did in real life.