As soon as she sees him roll off the shelf, she lunges to catch him. She manages to grab hold of his arm, but, unprepared for the sudden weight, she drops down with him. There being enough space between them and the floor for her to regain her wits, she's able to beat her wings with the strength and speed required to keep them from plummeting.

So instead of plummeting, they just slowly descend to the floor. It results in moderate strain on her arms, but it's a lot better than the man having broken bones.