Wait how does the body even see? In fact isn't it worse, she can't even see her own fingers, it could just get cut clean off!
She could be doing it by sense of touch. So long as her left hand is laying the scissors on the right hand's pointer and middle fingers, she'd know where her fingers are in relation to the scissors. She could also judge length via hand or finger width.
Alternately, she could be doing it in front of a mirror.
