Okay, re-reading this thread - if it is psychological, you need to get referred to a consultant paediatrician by your local doctor. And they can refer you to CAMHS. We had a year and a half of CBT therapy for our child at CAMHS and it worked. If your daughter can't see, you know she can't but you have to reassure her it will come back, even if it's not today or tomorrow. It will happen. The most important thing is to keep calm and actually treat her as if she can see: obviously to walk with her, if walking, so she doesn't bump into stuff, but try not to describe everything, because actually her eyes are working and sending visual signals to her brain - it's just that her brain is blocking the signals to her "conscious self" if you will. My child found they could occasionally get a notion of something that had just happened (a sign by the road) because their eyes had seen it, and told their brain, but they felt they could only see black.
re school, if at all possible, get your daughter into school every day, even if she can't see. Ask for any available teaching assistants to go with your daughter into classes and take notes so she is filling her day as normally as possible and not "feeling blind". If my child wakes up without sight, I go into the school myself and do the lessons with them, or get the material from the teacher and do the lesson in the Student Support Unit. It is very hard work, and emotionally very hard but very important to just be as normal as possible. The only concession to not seeing we made was to buy a very snazzy cane when there was a long period of our child not seeing, but it was rarely used. The most dangerous point was when our child lost their sight as they were walking home from school on several occasions and had to phone us to get them from where they were standing.
But the sight comes back. It really does. But you need to be in touch with the professionals. If there's any way of me and thee getting further in touch, I don't know how.