Heh. And we've just unlocked the earliest death in the game. Success. ^_^
Also, small gripe, why kill the small child when you can kill the soldiers who are in the process of killing you and the small child would be an excellent hostage and might(aside from a small case of bloodlust) be the nations only chance at the magical monarch it needs?
To be fair, who's to say she didn't? We were a bit distracted by our own imminent death, after all. Plus, we know she can blow pretty large holes in the walls of our castle with enough advance warning from our first run-through with the vault, so she probably doesn't really need a hostage to get out.
Also, because if we arrest her and don't free or kill her, she eventually gives up all hope for Elodie being a good ruler, from her perspective, and blasts her way out anyways.
EDIT:
Oh, and it just occurred to me, it's funny you should mention that Elodie might be the only chance at the magical monarch Nova needs. We actually learned in this run-through that there may be another Lumen in the line of succession. Charlotte is implied to be a Lumen due to her magical healing powers, and if Elodie dies, will become next-in-line as her father Laurent becomes King; Juli might actually know or suspect Charlotte's ability, since she seems to have quite a few friends for someone out of favour with the regent, though there's no real evidence for that. On the other hand, this also results in Queen-Consort Lucille...