Because her family was too large for Edward, a fisherman, to support, Agnes found employment as a young teenager as a waiting girl of all work at the Fountain Inn, a Marblehead tavern.
In the summer of 1742, when she was 16 years of age, she caught the eye of Charles Henry ("Harry") Frankland (1716–1768), the 26-year-old Collector of the Port of Boston, in town for business.
Agnes, Sir Harry, and Frankland's son from a previous relationship, Henry Cromwell, then moved to rural Hopkinton, Massachusetts.
She had no children of her own, but returned to England with Sir Harry's son, Henry Cromwell, to live with the Frankland family.
Lady Frankland's life inspired several stories about the tavern maid turned wealthy wife of a baronet, particularly due to her heroics in Lisbon.