Seems to be post-op if she is a tranny? Those photos don't seem to show a bulge in the wrong places haha.
I had a similar experience; private didn't advertise as a tranny but after the session, I came out thinking something was weird. I've never had a tranny ever, and had no desire for it, so I didn't know what to expect. Like your mate's experience, she seemed 100% legit, down to the voice, but the big thing that made me suspect was when I was fingering her and felt no G-spot. Driving back home I just started thinking, and started noticing all the little things that reinforced that she may have been a tranny, like her sweating (her back was getting sweaty!) and her pussy was tight and not very well lubricated, despite smothering my condom with lube already. But goddamn she sucked a mean dick. One of the best I've had actually haha.