Missy the Werecat
When puberty brings on her first Shift, Missy goes into the mountains for two years until finally learning to Change back. She can Change from fully human in one instant to a mountain lion in the next. Everyone assumes her two year disappearance was because she’d been kidnapped by a sexual predator that she managed to kill.
A thousand specially selected people leave a troubled Earth for a new start on a virgin world many years away. Their starship is state-of-the-art and entirely automatic; its passengers safely sleeping through the long journey. All possible scenarios have been taken into account except one. There is no way to predict sabotage.