[mighty]

The problem is that you're conflating incompetence with a lack of capacity for competence. In other words, the mere fact of not knowing something implies that one can never know it. If that were true, nobody would know anything.

What I'm saying is, you may well be correct in your assessment that she was incompetent for the job, but that assessment doesn't qualify you to make the further implication that's she's not smart, or inherently incapable of competence.

I've noticed you added the bit about her being indignant and suggesting that such knowledge was beneath her. That does suggest she would be resistant to acquiring domain competence, which certainly doesn't bode well even if your company was open to letting the hiree acquire it on the job. On the other hand, I can understand her getting pissed off about someone using such a question as a litmus test.