Tough call. She doesn't seem happy by the sounds of it - with the pacing and the calling and looking for a place she is secure. Also, IMO, she is highly prone to injury now.
She has feel and smell to go by. Not a lot. You could help by installing an electric fence - she may be able to sense the clicking of the electrical pulse that would guide her a bit. I know many people can feel it before they touch, and I figure a horse would be much more sensitive. Or put gravel down all along the inside of the fence - about 18" wide. She could definitely feel that. Other types of ground cover near the barn, edging on the walkways, etc. Think tactile.
If you live in an area where plants grow year round, you could plant different flowers/trees/bushes in different areas and she will learn to associate the smells with safe areas.
Tough call. But I think if it was my horse, I put her down.