Black Screen on Galaxy S5

My daughter dropped her Galaxy S5 in water, and now the screen is black. The phone works otherwise. I want to do a factory reset before I send it anywhere but nothing is working. I have tried using Kies but it won't do it. It finds the phone but won't let me reset it. Is there another way to do a factory reset when you can't see the screen?

ETA she had data off because she was in Italy at the time of the drop so we can't use Android Device Manager.

Thanks!