Her parents tried to save her but died, leaving the baby Garnet with two bodies in a boat. The boat was slowly brought to shore near Alexandria, where Dr.Tot found her. Garnet was accompanied with a horn, which was removed from her. The horn was the sign of a Summoner.
Being just a baby, Garnet was taken in by Queen Brahne. Queen Brahne lost her own daughter and named the baby after her daughter and raised her in her daughter's stead.
Garnet grew up with just images of an eye in the sky, until she first sees the ship Invincible and recognizes the red teleporter light beneath it as the eye. She swoons right away and realization dawns on her. Her village of Summoners was wiped out by Garland and the Invincible, in depserate attempts to rid Gaia, Garnet's home planet, of Summoners, whom could predict and withold the coming takeover of the other planet - Terra, where Zidane was created as a Genome to destroy Gaia, just as Kuja the failed experiment was to do before him.
Garnet, therefore, has her white magic skills and summoner skills like Eiko since they are both from Madain Sari. The only reason the power-greedy Garnet and Kuja wanted Garnet and Zidane, was because of Garnet's powerful and rare summoning powers and Zidane's successes in saving Garnet and the planet Gaia...
The Crystal has been Explained...
