Seller dies, and Daughter Refusing to Honor Contract

[H J.]

Situation: in 2017 I got a property under contract for $60k. Found a buyer, who paid $1000 earnest money to the owner. Owner was elderly, and his wife had passed away in 2010 without leaving a will. So estate had to go through probate. I got an attorney who did a lot of work(for more than a year) to get it through probate.

Around the end of 2018, this elderly owner got Alzheimer's and died. Now his daughter is refusing to honor the agreement. She is claiming that he had dementia at time of signing the agreement, which is not true.

She is demanding that I remove lien on the property.

What would you do in this situation? Thanks in advance.