Wait, so she reloaded a previous save state of her body? Was that permanent? Is she now as strong as she was before the reset? Or did she only temporarily gain that ability? I'm rather confused.
Clearly not permanent - she got big and then got little again, even our prospective murder victim noticed that. Whether that's part of the way the command works I don't know - she could have used it again to go back to her young form, or it may have been a timer or that she ran out of MP or something.
I'd guess that it's something which has a time limit or which can be cancelled manually, but which doesn't reset everything completely when it ends - otherwise it's not going to be very useful in an emergency when she's at risk of dying . . . So retrieve a saved state, finish the fight, heal up, and then cancel it having healed yourself - gets you out of a tight spot and lets you heal, but at the cost of some MP.
It does feel a bit like a cheat power, but it's not like she's playing the game the way it's supposed to be played . . .