Sandra Barkley is introduced in the episode "You're Lookin' at Country" when she appears at the CMA Awards with her husband, Carl, as guests of Avery and Juliette. Carl clearly is dissatisfied with Avery's choice of girlfriend but Sandra acts more kindly towards her and tells her husband to behave himself.
When Avery speaks to his mother about his future with Juliette and their unborn child, Sandra advises him to do what he believes is right so Avery decides to propose to Juliette and she accepts.
After the birth of Avery and Juliette's daughter, Cadence, she shows up at Juliette's house to help out with her granddaughter, which is something that clearly makes Juliette unhappy. Sandra advises Avery to give Juliette time to adjust to motherhood.