Missy the Werecat by P. G. Allison
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. She keeps her werecat nature a secret. There is no pack, no pride of other werecats and no alpha. She’s a girl with fantastic abilities growing up and learning to do great things in today’s world, amongst humans. She only has her instincts to guide her and those drive her to train herself to extremes. She must control those instincts; dampening the wild predator is often necessary. Her raging hormones and enhanced senses require very strong controls; she explores what happens when those controls are relaxed.