Ha, I've been unable to figure it out either (after 4 playthroughs). I also noticed that her missle count and energy were going up as she did it (I think).
It's known as The Crystal Aura/Flash.*Spoiler* You hold down DOWN, L, and R while seting off a super bomb. It cost 10 missles, 10 super missles, and 11 super bomb to do it. You also have, to have less than 50 units of life and then your missles are converted into life units.