Morgana was simply hoping getting back out into the hallway would give them a chance to escape the rush of water; the hallway, hopefully being not quite as full, or as deep.

"Would that not be one floor --" she's about to say up, since there was that fall, into the pit where the little girl's skeleton was found, but when he loses his footing, and goes under, he pulls her with him.

In a frantic attempt to stay above water. She lets go of his hand.