It wasn't the first time he'd been tossed around like a rag doll by a powerful being with magic, let me tell you. But that didn't make it hurt any less. Harry hit the water with a splash and a sprawl of limbs, his staff more or less tumbling out of his hands. He let it go, since he didn't actually need it for his magic uses, and was up and on his feet as she approached. The Winter that was inside of him roared, but instead of crushing the girl, Harry forced it back. His breath turned to frost with each exhale and the predator within paced. The cool thing about Harry's magic training meant he learned to ignore pain, and with the Winter Mantle attached to him, he didn't even feel it until much later.
She could hurt him. Harry wasn't going to hit her back. She was just a kid and she was already hurting. He'd never justify causing her more harm. But he brought some quasi Latin phrases to mind, because while he wasn't going on the offensive with her, it didn't mean he was stupid enough not to defend himself. If she thought he wasn't comparable in terms of raw power, that was her own mistake.
"No," Harry said, "you didn't choose any of this. The only thing you get to do is decide where you go from here. It doesn't magically fix what happened to you," because something obviously had, "it doesn't change the past and you don't get to re-do anything and people will probably use your past against you for the rest of your life, no matter how much you try to get away from it." That was the truth, harsh as it was, he wasn't going to offer useless platitudes or promises that were false. He was straight forward and trying not to be condescending about it. " But you can set the course of your future. You can be what others believe you are, or you can be what you want. There's always a choice."
Harry himself had been the target of the White Council's scorn since he was 16 years old, and broke the First Law. Thou shalt not kill. He'd murdered his adopted father--who himself had been a dark wizard--in a blaze of fire, and since then they'd been waiting for him to flip the switch and become the maniac they imagined he'd be. That he'd harness that dark, seducing power at his fingertips and destroy the world with it. Harry defied them, but that didn't mean there wasn't a contingency plan in place to execute him the minute he crossed the lie. They'd come close on a couple of occasions.
Harry spread his hands to the side, "You can kill me, I won't stop you." But he'd sure as shit lob his death curse at her the moment she did and take her out with him. Or at least hamper her magic enough so she wouldn't hurt anyone else. The nature of a wizard's death curse worked that way. "But if you don't, I will do my damnedest to help you while you and I are both here."