It's necessary to the completion of the transformation. The timing varies.

[At the last he hesitates, though only slightly. It's likely Raine was preoccupied enough with tending the townspeople to have missed some of his more destructive actions during the fight in Luin. Banked wings were obvious enough, even if his real use of them had escaped her attention.]

Doubtful. She won't be able to use it until the transformation is complete, regardless. It's a state that can only be achieved if the wings are properly attuned to the person.