So the correct summary of this situation is that you have a 12 yo open broodmare that hasn’t been ridden in 4 years that you are not willing to ride, not willing to pay to have rides/training put on, not willing to ship to an area with a better market, not willing to lease or consign and doesn’t suit your local market?
And you want to know what a fair price for her is as is?
I believe that is free to a good home.