She would surface, squeaking and clicking at Luigi. While they say "sky's the limit," safe to say Luigi won't be airborne. Not without proper power-ups and other safety measures. She was making sure he was okay in the end...

She had some solutions, catch him on her backside as she shapeshifts into a dolphin again, throw him a Winged cap, or pray he has a power up that's gonna make him land safely. Until then, she's in a state of panic.

And then a LOUD dolphin squeal, and loud clicks.