
The answer to both of your questions, let's say it'll happen very soon, when they get her body back from the enemy
SPOILER
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It's when the the bird gets poisoned she'll return to her original body, basically when one of the bodies ( the bird or the human) is unconscious she will switch to the other body, and she'll eventually be able to switch bodies by using the poisen and it's antidote

SPOILERS
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"Later, the Granor army claimed to have Zelle's body and threatened to kill her if the Roymond army attacks them. As the only known royal heir alive, Zelle is very precious to the Roymond army. Valhail managed to start a surprise attack, win the battle, and reclaim her body alive. However, they found that she was poisoned and would die in 30 days without an antidote. Bird Zelle got frustrated and bit her body on the neck, trying to wake herself up. Then Zelle flew off and was shot by poisoned darts after getting lured into a trap.Zelle woke up as human again."
After that A LOT of things happens before she return to being a bird again so I'll just keep the spoilers at that
When does The hot guy(I forget names easily sue me) find out she's there princess?
Also when does she turn back to being a human?