Not "equally absurd." The stated assumption is that the general case is more like the parent-child case than the axe murderer case:

True.

Also, are you actually saying the young orphan will be better off dead?

I'm saying that the marginal person on average adds negative net value to the expected utility of the universe as evaluated by me. As well as pointing out the negative utility of an orphan starving I point out that a saved life can have negative externalities as well as positive. In this case it was to the other orphans who lose some of their resources.

A negative externality that I place the more weight on is the contribution to existential risk. I do discount the far distant future but not to the extent that I don't consider existential risk at this critical stage of development to be pretty damn important.

Is that what she would choose, given the choice?

This isn't fallacious since the argument behind this line of questioning is implied rather than explicit. In most cases the reasoning is not even noticed consciously by the author or many readers.