Fantasy - girl gets powers, possibly demonic, the older you are when powers manifest, the more powerful you are. She is assessed and it wasn't clear which side the assessor was on.

[Beckoh]

I remember someone coming to assess the girl who has developed powers, who turns out to not be clearly good or bad. In the book, the older you are when you develop powers, the more powerful you likely are. One of her powers was either bringing a bird back to life, or creating a bird. The assessor told her never to tell anyone about that.

Later in the book the girl attends a party and all the humans with powers wear black with more colour/white to show how powerful they are and are displayed by their owners, who may be demons if I remember rightly. The assessor is later imprisoned and he then escapes after trying to help the girl.

Not a great deal to go on, but it was the first in a series I think, and I wanted to find the rest in the series and never got around to it. Likely read on kindle at least 5 years ago.