Pretty good way for her to lose business asking something like that! That also can fall back on you. Some guys may wonder why you were doing doubles with such a gal.

Best way to handle it, if you are going to continue to do doubles with her, is tell her not to say such stupid things.

If you were just saying that you were with him and then she was with him separately, did she ask you this question? I assume she told you as you indicate you answered back.  

Either way, maybe talk to her about appropriate conversations to have with guys (which includes what she shares about self to them as well) and if she was gossiping to you, she shouldn't do that. It gets around. Big difference to ask such a question between providers without the other knowing who she is talking about, which you obviously did know who.

Like I said, I am not sure if you did doubles with her or if she was talking behind his back to you?  

Either try to help the newbie out, which is what I would do, or cut her off. Must learn how to converse with the guys so you don't get them thinking about anything that would make them feel guilty or pissy.  

We all make mistakes, maybe talk to her and help her. If she doesn't listen, then that is on her and stay away. Things come back to others (including you) if she is doing things screwed up.

I once asked a regular how his job was going. Oh shit! He went on a rant for a good 30 mins. Now try to do the appt with him being all mad and trying to calm him down. Ugh. Worked in the end, but barely.

I always watch what I say. When you have experience, you don't have to think before speaking. Newbies have to think and process before saying.

Asking dumb questions like that will not be good for her. How would she like it if he asked her some personal questions like "Don't you feel weird doing this with a SO?" or "How do you feel sleeping with so many guys?" sort of stuff. Not trying to be offensive but like we can judge them.

I know MANY men who seriously love their wives and just want some. Not anything more. You gave the right answer.

Help that newbie out so she doesn't fuck up her rep.

...I'd light her up pretty good. That is a very inappropriate question to ask any client. I have been asked about my wife since I wear a wedding ring and people are genuinely very curious about my lifestyle, but there are some things never to be said out of plain old common sense. I don;t care how new you are - that's just a stupid thing to do.

If a customer is married, but doing it in an accusatory way like that is WAY out of line.  It sounds like she's your doubles partner, so you should exit before she damages your business.  If she want to blow up her own biz, that's her choice.  

Of course, if it happened to me, I would put her on the spot and say, "Why do you like being the other woman that somebody is cheating with?"

And projected it onto the client. A question such as that comes from a place of resentment, or worse. If a lady asked me that 10 years ago I might have laughed it off. Today I would walk out and never darken her doorstep again.

was developed just for questions like that.

Ummm NONE OF HER BIZ we are not the marriage police!!!
I ask guys on my site to please not take off their wedding ring.
I do not care about why they are cheating, if they are cheating etc.
I'd rather not have them risk loosing their ring thinking I give a shit if they are married.
We are not dating -  
I do not judge.
I do not care about their wife or their reasons/excuses/choices to break their vows.
Just come enjoy time together and leave the personal shit personal!!
I have had many guys offer up why they cheat- which actually I do not mind hearing only because it allows me to understand where they are at in their life a little (meaning wife does not do anal and its on his bucket list before he dies etc)
But NO if a guy never brought the subject up, I would never in a million years EVER think to ask
totally out of line...
Oddly enough, when I was married - I always wore my ring, some guys would actually ask me if my hubby knew what I was doing!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
I do not care if they ask, but did seem a little funny!!!!

Yeah, I'm a 100% if someone I was doing duos with said that (and it was my client), I wouldn't even give the client time to say something, and I'd throw her ass the fuck out. I don't know what kind of fucked to morality you'd need to have in order to be a sex worker and judgmental about people fidelity.

On a side note, while I doubt it's the case here, Simone could honestly be doing research. There was an amazing ethnographic study done by Katherine Frank (put into the book G-Strings and Sympothy) that asked anon. club patrons  questions like that. Depending on how far along I am with my doctoral work at the time of my exit, I plan on doing similar to examine the same systems in the hobbyist world, though clients would be made explicitly aware of that for ethical reasons.

What's the best comeback to this question?

"Let me guess.. you're a grad student?"  

"I dunno. Why are you selling your pussy?"

Or?

I think too many people are too easily offended.   I found that if I don't want to answer a question, I don't answer it (unless the judge is threatening contempt charges.)