at the end of the day every single prossie works her own way. Some pay tax and some don't. Some use a baby wipe and some don't. Some actually shower between clients and some don't and some of us like or in my case need a gap of at least 45 minutes between clients to relax, freshen up, re do hair and make up answer calls and emails or just to sit and read for a little bit.
You will only have the prossies word unless of course you know her quite well and know for sure of how she works. Speculating about it gets you nowhere as you will only know if she showers once you arrive and can smell she is fresh out of it or see that the ends of her hair are wet where they fell out of the bottom of the shower cap.
Just because one does it one way it does not mean everyone does it that way. Some of us will happily take bookings back to back yet some of us will say oh sorry can you make it at quarter past instead so I have time for a shower and a drink. Yes we do it to earn money but not everyone Is willing to forego their own feeling of cleanliness for a few extra quid.