Yeah. Mir's body is entirely artificial and created by magic, and if she doesn't get a 'keep alive' signal every six hours or so from Ar Tonelico, she dies instantly. It's a feature, not a bug, intended to keep her species under control.

ETA: That signal has a limited range btw, so she can't go everywhere in her world she might want to. That does impose some limits on her actions in canon.