"Oh you have not," she replied with a roll of her eyes. "And honestly, if that's how you're going to go about teaching, you'll have your students crying into their cauldrons on a daily basis." She reasoned that actually wasn't so far from the truth, which got her wondering again what had prompted him to start teaching in the future.
Still, it was a touch vexing that he could so easily reverse her spell. Then again, he'd likely had more cause to learn things like this. More reason, at any rate, and likely nothing so petty as her reasoning.
Pressing her lips together, she focused on the water and pretended the glass wasn't even there because it didn't matter in regard to her intention. Focusing entirely on the water, she cast the charm again. This time her lips didn't move, and only the water was frozen.
She relaxed her shoulders slightly before she glanced over to Severus for his approval.