Karen's elderly Uncle Joe gave her written authority to sell the family house. Uncle Joe lived in Maine and Karen lived in Minnesota. After about two months Karen found a buyer for the house and signed an acceptance of the offer on July $21.$

Later that same day she learned that Uncle Joe had died the day before $($July $20).$ Other members of the family did not want the family house sold and claimed that the acceptance Karen signed was void because Uncle Joe had died prior to acceptance.

The buyer of the house claims Karen had the legal authority to sell the house and that the contract is binding.

Who is right? Please explain.