Context: Caedus sees Luke's face when he's fighting her, and we are told that Luke has mysteriously "zoned out" at around this time. Then Luke comes back out of his trance, Caedus sees Jaina, and Jaina loses her amp.
Ehhhh not sure exactly where, although here is a brief snippet (no preview for that page) of where Luke goes into his trance. No idea why tags aren't working.
I think it's very clear that Luke was amping her, and possibly to the same level as himself since Caedus honestly thought he was fighting Luke and didn't think he was super weak or something.