I feel really sorry for the mare especially, because she can't help it that she can't see, and now she is in a place that is scary for her, and she may not be able to stay either, so she will have to learn a whole different place again if you move her.
What a sad situation for both of you. I feel like the place you got her from should have known something wasn't right.
I did hear of a rescue one time that specialized in blind horses. It had a funny name that had something to do with dogs, but it was a blind horse rescue. There were in the mid-west and moved back east. I didn't look where you are at, but maybe it's something you can Google.
Oh, here, I found it:
Rolling Dog Ranch Animal Sanctuary