"I've got you!" At this point, being quiet is the least of Allura's concerns. If someone comes over and shushes her, then she'll accept her scolding. Better that than turning a blind eye to danger.

Instead, when she sees him starting to fall, she moves to catch him with arms outstretched. Which might seem like a good way to get knocked over, but she's still quite strong despite her small frame. And no offense to Luke, but he seems to have a lighter build too, at least compared to some of the other men she's met.