It's actually, sadly, quite easy. In her mind there are no shades of grey, no systems, no circumstances. There are people who are Good People and people who are Bad People, and which people are which is self-evident and not as related to their actions as you might think. It's just a case of identity. They're Good when they do bad things, and Bad People are bad even when occasionally doing good.
And so celebrating the death of a Bad Person is honorable, obviously, and celebrating the death of a Good Person is sickening and deplorable. Clearly.
And if I agreed that this was the way the world was, I'd probably agree with her. Unfortunately for me, that seems fucking nuts.