This comment bothers me for two reasons - one obvious, one not so obvious.

The first is that I think you're empirically wrong - I think Swimmer963 will make an excellent nurse. She is obviously way above the mean in both intelligence and determination, and there's not much more to success than that. When she says she is "terrible" at something, she is probably just being 1) modest and 2) self-critical - what she probably means is not that she's worse at it than the other people in her cohort, but that she realizes she can be a lot better at it. That kind of realization is the sine qua non of excellence.

More abstractly, I think your comment is problematic because it tends to undermine or second-guess a difficult choice that someone has made after the fact (in this case, Swimmer's decision to become a nurse). This is non-obvious from a rationalist standpoint, but you really shouldn't do that. The most obvious example situation is that you don't tell your friend that you think he was a fool to get married when he's already married - you can give him that kind of advice before the wedding, but not after. If Swimmer were asking for advice about what career to go into, it would be reasonable to suggest one area or antisuggest another, but she's already made her choice, so this kind of advice is not very helpful and may actually be harmful.