The joke I think is that she seriously underestimated the task. This is the moment where she's realizing "Well, that didn't work" while the mammoth is still processing that a tiny woman has apparently stabbed it and will presumably kill her in a second.
Best case, this is an absurd warning about hunting large animals on one's own. The humour would be that this woman, rather than killing the mammoth, is about to get stomped. Or a at the very least, a terse "Do you mind?"
Worst case, this is intended as "Strong independent (cave)woman don't need no (cave)man.", and in acting without said man, she has proven said maxim wrong.
I'd like to think there's enough wrong with that thinking that even the most ardent misogynist ought to find a step too far (people hunt in groups, so she would have taken friends along, surely?), so I expect the intended humour is closer to the former than the latter.
The choice of a female protagonist is an interesting one though.
It must have been "Do you mind?". And absurdness of hunting alone.
Also i see nothing interesting on choice of female protagonist. Contrary to popular myth, women hunted together with men (based on evidence of broken legs) and had no strongly separate roles (like women being gatherers and men hunters).
I got a boxed set of most of his books off of Amazon a couple of years ago and have been supplementing it since when I have a few extra dollars to spend. I think I have one book left to get.