I have no experience of that so no idea. sounds like she should be paying you. for me that would be what would happen if were tortured for info. each to their own, I have no judgement. just no idea as no experience.
since you bring it up, what do you get out of it? is it physical or psychological?
I tried both just because I was curious and will basically try most things once. And I mentioned them here because I thought they were the funniest in the context of this thread
I did let a girl do me up the arse once and I won't do it again - it yielded neither a psychological nor physical thrill.
The watersports on the other hand I unexpectedly loved, although I only do it very rarely because it takes quite a proportion of a booking. I think it was that I found it sensually intimate or something. Either that or it was a release of my pent up anger at all women, an indication that I felt so in control that I could even have her urine as my plaything. FFS someone will google that now and doubtless find some Millie Tant figure actually spouting that bollocks I just made up as fact!