Petranne didn't know what happened to her brother. He was gone, that's all she knew. As she got older, she started to feel bitter to her sister and Aly. After all, if Aly and her spies hadn't been whispering thoughts of power into the regents ears, they wouldn't have thought to become king and queen, doing away with the boy-king and her little brother in one mage-brought storm. And then Dove took the place her brother would've. It was Dove's name the Isles rebelled behind.
In the back of her mind, a whisper of thought says 'The regents would have done away with them eventually,' but she hushes that. After all, she needed someone to blame for a life taken too soon, and she can't blame those already dead.
This made me tear up. Petranne was sort of forgotten in the books, and she lost her little brother so her older half-sister could take the throne. She must have blamed someone, and there was Aly and Dove, perfect figures that she can blame but would never do anything to harm.
Was her name Petranne or Petranna? I've only read the books once, compared to the 7 times of the quartets.