Shush, it's Nunnally. They didn't give her a Knightmare-piloting manga for nothing. Her superhuman senses will be enhanced.

If you ask for a serious opinion, then Kallen? Other than her, Millay? considering her family developed Knightmare Frames way back when...she could've learned a thing or two. And she did like the guy, knew his identity, etc. We just need the most unlikely plot exposition ever.

Or maybe it's not a girl at all and he pilots with Tamaki. It's possible.