It's "couldn't", not "wouldn't". As in it would have been physically impossible for what she described to have happened if she was dressed the way women in her position would have normally dressed at the time. Obviously not a beyond a reasonable doubt argument, but it's one more reason to have some doubt about her story.
This seems like an argument from stereotype.
The stereotypical 1990s congressional aide wore pantyhose, which casts doubt on this atypical narrative.
If we're going to apply that stereotype, can we apply others? She wasn't wearing hose, so that means she's probably a slut, and this is probably politically motivated regret sex rather than rape-rape?
The stereotypical rape victim tends to suppress the event, misrepresent it, change her story a lot, and refrain from aggressively pursuing justice, which explains almost all the discrepancies in what is in fact a true story?
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Hell, maybe she
was wearing hose, and the elasticity of the gusset allowed some digital penetration anyway, and over the years her recollection has mutated to omit the hose (since they didn't actually prevent the rape).
Maybe the stereotype we should be applying here is that women often misremember and misrepresent things, and it's important to #believenowomen.
Or maybe we should be stereotyping Joe Biden as an rich old white man in a position of power over a woman.
Or maybe the fact that she hadn't tied an onion to her belt, which was the style at the time, is a red herring.