She seemed relieved that he had given her this simple task, and quickly complied, grabbing a bucket of water and beginning her focus.  To be expected, she effortlessly manipulated the water around the tennis ball and moved it around herself as if she were dancing, the fact that she seemed amused by it was kind of...cute. So she could at least move an object with mass in her water manipulation, but could she do it with multiple objects?  She had done it with the rain earlier, it couldn't hurt to see how much multi-tasking she could handle with a few tennis balls.

"Good, keep manipulating the ball exactly like that," he stepped over and reached for another tennis ball and grabbed it, "We're going to add more to the equation now, I'm going to keep adding tennis balls, when I add a new ball, use a new way to manipulate that ball different from the first ball.  The moment you lose concentration is when the exercise will be over."

He smiled at her, "Be creative, have fun with it," he rolled the ball over to her, "Go."