Daniel signs a written contract with Mary to build Mary a barn for Marys horses with payment of $10,000.

Daniel and Mary sign a written contract on September 1, 2020. Mary pays Daniel $10,000 and Daniel begins to build the barn.

On October 15, 2020, Daniel tells Mary that building the barn is taking more of Daniels time than he originally expected.

Daniel demands that Mary pay Daniel $3000.00 additional money to finish building the barn.

Mary feels pressure to pay Daniel the $3000.00 for Daniel to complete the barn because her horses need a barn for the approaching Winter Season.

QUESTION: By contract, does Mary need to pay Daniel the additional $3000.00 for Daniel to complete building the barn? What legal theory applies to this case?