Most surgeons seem to suggest that if you can orgasm before GRS, you will likely be able to after; I'm not sure anyone's put a concrete statistic to it, but the vast majority of post-op trans women I've known have been at least as functional afterward.
(And yes, I can; it happened 3 weeks post-op while dreaming, but it took me a few months to figure out the new bits when I was awake. Still, I have no complaints.)
Keep in mind that something like 75% of cis women can't orgasm from intercourse alone, too.

So if they need a little help beyond a guy jackhammering away... it's normal and expected that some trans women might too.