I don’t have a date of birth for her, but 1325 would be closer to her mother's date of birth than her own. "She was very young at her father's death [1261], perhaps seven years old." Margaret was the daughter of Thomas Stewart, 2nd Earl of Angus and Margaret St. Clair (dispensation to wed 1353). In an arrangement with her sister Elizabeth, she took the title Countess of Angus and Mar [SP I:170-1].

Jim