This might be my favorite senshi awakening in any incarnation of the series, because I think Ami could have done it even if Luna wasn’t there. She reaches for the power before she knows she has it.
Ami loves Usagi so much already. I think just the word friend is enough fo Mercury to grasp who Sailor Moon is, because only one person would call her a friend right now. And that person is so dear to her, she can’t let her be hurt.
So she breaks through her brainwashing. But she doesn’t stop there. She needs to save Usagi, dear sweet Usagi. All her love (so new but strong) and all her rage call her power to her. Ami calls out for Usagi, and Mercury responds to save Serenity. (I love how Ami/Mercury transforms and goes through the entire speech before being shocked by it. Crystal is doing such cool things with SilMil memories.)
(Also, I have to go back and listen later to see if the monster *does* actually say she’ll send Sailor Moon to heaven, because if so there’s an angel/heaven connection that I think Ami made)