Her back is to him, so she knows he won't see the small grin that elicits--it's a fair enough thing to say. But it also gives her an excuse to turn around, which she does (expression smoothed out to a more amiable interest), deftly enough, so that she can take a few steps backwards. It requires a little more concentration, but she wouldn't be up here if she weren't confident in her ability to stay up.

"I'm doing okay thus far. You want to give it a try?"