Her hurting Nam with his guard down does seem more impressive than Yamcha's performance against Jackie Chun in retrospect... but then again literally all it took was a delicate chop to bring her down (and Nam didn't even have his eyes open either) so I have a hard time taking it seriously... and I don't think it was meant to be taken seriously either.
Let's just say Yamcha finds a way to humiliate himself like... he accidentally touches Ranfan's breasts and Bulma yells at him... then Yamcha drops the match like a bitch.
I have her at two thirds of Nam, because, when he was missing his youki (one third of chi), she could fight him and, when he focused, he one
shotted her in a way that reminded of Beerus vs Whis (1.5x a gap). Yamcha gets stomped.