She's coming back

she's coming back is Disc 2, Track 7 on the Xenosaga III: Also Sprach Zarathustra Original Sound Best Tracks album. It is a remix of here she comes (KOS-MOS) from the Xenosaga II: Jenseits von Gut und Böse ~Movie Scene Soundtrack~.

It plays when KOS-MOS ver.4 awakens to help the party fight off the Black Testament on Old Miltia.

In Project X Zone 2
A remix of she's coming back was made for Project X Zone 2. It plays at several points in Chapter 6, 'You Will Know Our Names' (itself named after another Xeno series music track), such as when KOS-MOS arrives at Rennes-le-Château at the start of the chapter.