Many of the characters have issues like this for their final deathblows. I find what works best is to alternate between using her top four deathblows in battle (including the one you're trying to learn). Elly is always pretty stubborn about it I'm afraid. Billy is the other one who gives me trouble.

Also, you do get to see the world map in Disc 2 just at the very end. There are actual side quests in the second half.