It's been a while, but I thought there is a point later in the game where Terra rides in MagiTech Armor again? I could be mistaken, however. And as for cannon, I don't think they say what it looks like, but there is a little sprite of it shown whenever the she first wakes up after having it removed by the man in Narshe. It's also briefly shown in two scenes in the opening cinematic sequence for the PSX version of Final Fantasy VI where it looks like a small band around her head.
