No man ever steps in the same river twice, for it's not the same river and he's not the same man.

— Heraclitus

I assume the OP is asking, in jest, if the same applies to women, and having sex with instead of stepping in.

Personally I think it's the same ship or axe, and the same person, even if it's not the same physical object anymore, because “my grandfather's axe” means more than just this specific combination of head and handle, and has more to do with the history and sentimental value of the thing, and what it meant to my grandfather and what it means to me.,

And that while it's obviously not the same water or even, if the river meanders and you wait long enough, the same river bed, a river is more of a geographic concept than a physical thing, so, yeah, it's also the same river, inasmuch as a river is a thing.

(As for the first part, sure, of course women can step in rivers, be they or not the same one, same as men, just as they can own ships or grandfathers' — or even grandmothers' — axes.)

I think a shower head would make more sense, though, unless the river has some safe but high pressure enough rapids. Or if she considers the fish part of the river, in which case, ew. But maybe it's more of a platonic thing, what do I know.