Acorna's quest - Anne McCaffrey

Found as an infant drifting alone in an escape pod in deep space, Acorna was reared by three young asteroid prospectors who raised her as their mascot, their miracle girl, and saved her from those who would destroy her mysterious powers.

But now Acorna has become a young woman who has dreams of a shining world with blue grass and green skies. She still has the translucent horn in the middle of her forehead - she still has her powers to make things heal, and grow, and purify, but she longs to know where she came from - what world in the galaxy was her home?

With one of her old protectors, she sets off on a quest to find her own kind, but even as she leaves a strange craft appears in the skies, peopled by gentle and mysterious telepaths who bring, not only terrible news of a frightening race of invading space killers, but also the memory of an infant, lost in space, long ago...