“Do you want to build a snowman?”
If we think of Elsa’s magical power (which primarily makes ice, but can also somehow conjure gossamer dresses, apply eye-shadow, and animate snow creatures) as a natural talent (something like our temperamental inclinations), then the question of integration becomes one of how best to “train” this power. And, the controlling or training of a power is a matter of acquiring the corresponding virtue.
Now, someone is good or bad primarily because of the virtues and vices they have and not necessarily because of genetic, temperamental, or environmental predispositions. These impulses of themselves are morally neutral. So initially, Elsa’s power isn’t particularly good or bad, it’s just powerful. Where the moral character enters is with the stable virtue or vice that shapes the power. And this is precisely why the “Lock her up” approach is so crazy . . . the only thing that it habituates is the very fear which the Grand Pabbie (the aforementioned troll king) identified as her enemy.
So with Elsa, the question becomes one of how to acquire the virtues to apply her power well (making snowmen, hosting winter festivals in season and out of season, playing snow mountain hopscotch, etc.) and thereby channeling the power to a good end and eliminating the occasion for potential abuse or harm.