Space Symphonic Poem Maetel ~Galaxy Express 999 Side Story~(2004)

Uchuu Koukyoushi Maetel: Ginga Tetsudou 999 Gaiden

Maetel abandoned her mother and her home planet, the doomed and frozen La Metal, where people must become cyborgs to survive. When she is beckoned to return, her options seem slim: follow her mother's path (and with it a robot mind and the contempt of all humans), or run away and fight with humans against the machines. Yet, she is not without comrades and defenders. If she can accept the friendship of beings of metal who desire peace, and oppose those who think being made of flesh and blood is enough to make one human, she may still have a chance to find her own path.

(Source: Anime-Planet)