If familicide by itself can't determine a character's alignment, which it demonstrably can't, then no individual act can determine a character's alignment. If you want to claim that Hilgya's forbearance is a Good act, make the case (for the record, I don't buy it - it is neither a personal sacrifice on her part nor done of the sake of the dignity of sentient beings), but it alone says nothing about her alignment as a whole.