Trin has been raised with the knowledge that her parentage was unknown and she was human. Those two items were the cornerstone of her existence.
An altercation at a baby shower leads to her discovering another side to herself. That side was big, crystalline, and caused the other dragons in her vicinity to bow their heads. Defending her friend had led her into this new shape, and now, she was stuck with it.
Taken to the central hub of the dragon council, she trades her cooperation for knowledge and freedoms. She had been an independent woman a lot longer than she had been a dragon, and she wasn't going to lose her lifestyle just because she could suddenly breathe blasts of pure energy.
Along the way, she learns about where she came from, and it gives her an outline for the life she wants, with the dragon of her choosing.