On Thu, 2 May 1996, Isabel Arantes wrote:

I don't beleive we've ever seen her actually use the katana in combat,

though I may be wrong.  But the general assumption is that she's VERY
good with it.
	Actually, when Nodoka first pulls out her katana from
the 'case' she keeps it in, it slips out of her hand and almost
hits a terrified Ranma-chan. who happned to be BEHIND her at the
moment. :) Tgough we'd like to think Nodoka could do a neat
and quick seppuku, she porbably doesnt know the first thing
about using katanas.

Let me rephrase that (and keep i mind that even a trained swordsperson 
can slip up when gesturing with a heavy blade ^_-):  Our only evidence as 
to her overall skill is Genma's unreasoning terror of that blade, by 
which we can assume that she at least knows SOMETHING about using it, 
since Genma's the only one would would have occasion to know. ;)

I think it's one of those things though that's never really answered so 
you can assume either way in writing a fanfic. ;)