What happens to a discharge of mortgage document when the property is sold in a county auction?

VERY long story short, my 68 yr old mom owned her home for almost 40 years and when the upkeep on it became too much of a burden, she filed bankruptcy on it and began renting. After bad (or simply lack of) info from her bankruptcy attorney, she found that the home was actually still hers, just not the debt. 3 years later the county or bank or whoever finally got off their rear ends and put it in the auction, & it sold. She never got any kind of documentation from the county or bank saying the house is no longer hers, though I see a "Certificate of Foreclosure" listed on the county deeds website. Now, three months post-auction sale, she is receiving a letter from some title office saying that "They have recently acquired an original discharge of mortgage document that needs to be recorded or the lien will always stay with the house". They want $40 to have it recorded, and they seem to think it's her job to pay it. What if she doesn't and ignores it? I'm so sick of this problem.