yay! I'm smart :D
but... why do we have to go through all of the other answers?
(Hi I'm Penelope.)
It's mostly because we didn't want to punish the player for guessing right by having them miss a substantial amount of content in the final scene! This game was a jam entry, so we didn't have the time or resources to really make the interactivity more than a gimmick.
But even from an in-character reason, there's a very good reason why Leila waits till the very end to pick that option:
<spoilers below, everyone!>
...she's very much trying to rationalize away the truth/procrastinate a confrontation.