If she had part of her body in contact with water, Yin could use her spirit to look at a book - and according to the omake in the manga, she can read. As she is, lying there without even a glass of water... she's only pretending to read.
They never state that she's blind, but in the eps where you see her flashback it's suggested quite a bit. Like her asking if the moon is full, why would someone ask if the moon is full if they could see it. That and she's usually pulled around by her hand most of the time, though she seems like she wouldn't run without being pulled lol.
Well in the dub she asks if the moon is full because she noticed the lighting of the room. She doesn't want her Mom to turn on the lamp, because she likes the glow of a full moon.
She says she can tell without even looking, that the moon is full, because she loves the glow it gives off so much.
Plus she sees her instructor and her mother both reach for the pen light and touch hands. She also sees her mother lean closer to her instructor and the she runs out of the room because she feels her mother is trying to replace her father with this new man.
I'm pretty sure she wouldn't have ran away if she was blind, she wouldn't have been able to see them.
