As her husband's sole heir, she inherited his business and soon after his death married his chief clerk, George Hayley.

Unusually for women at the time, she became a benefactor, donating money and goods to charitable endeavours, and ran a whaling business.

[3] Her siblings included Sarah (1721-1767),[2] known as Sally, who was said to have been the inspiration for Charles Dickens’ character Miss Havisham in Great Expectations.

[4] Among the others were Israel III (1722–1805);[2][4] John (1725–1797) a prominent politician;[5] Heaton (1727-1803)[2] born 20 months before Mary;[6] and Ann (1736–1750), who died from smallpox at the age of 14.

[21] While her husband ran the businesses, Hayley continued to indulge her interests in intellectual conversation, attending trials, travelling widely[22][23] and going to the theatre.

[13] Mary Hayley brought her husband into the social and political circle of her brother John, and though George was taciturn in public and in their private life, he was aggressive in his business dealings.

[32][33] As such, when Rotch's ship the Dartmouth delivered a shipment of whale oil to London in 1773, it was Hayley who arranged for tea to be loaded for the return voyage.

[19][Notes 2] Since the governor of Massachusetts closed Boston Harbor as a result of the rebellion,[39] Rotch and Hayley, along with Alexander, Benjamin and Richard Champion; Thomas Dickason; Samuel Enderby and Samuel Enderby, Junior; and John St Barbe formed the British Southern Whale Fishery,[40] also known as the South Sea Whale Fishery.

Rotch negotiated with Hayley to market the whale oil and after travelling to London to secure government protection of their ships and crew from seizure, joined the fleet[39] off the coast of Brazil.

[47][48] Hayley proved to be an astute businesswoman and by routing her funds from America, through neutral banks in France, was able to reclaim a large portion of her nearly £100,000 left from George's investments.

In 1783, Dinah had married a captain of the Devon Militia, Robert Baker, whom Hayley considered a fortune-hunter because he was deeply in debt.

After arriving in Boston and hearing of the impending birth of her first grandchild, Hayley sent money to the couple and a conciliatory note.

[51][Notes 3] Upon the conclusion of the American Revolutionary War, Hayley and Rotch made a plan to sail for the United States to attempt to collect around £20,000 still owed to her.

[12][48][54] Hayley wrote to her business partners informing them that she was leaving Alexander Champion, junior in charge of her affairs in London for the duration of her sojourn abroad.

[57] Hayley, who may have accepted an offer to stay with Dorothy Quincy and her husband John Hancock when she arrived,[58] took up residence in Boston, leasing a house and fitting it out with a collection of American furniture and artworks.

[59] She was quick to pursue relationships with her business partners and gain a favourable reputation with Boston's elite through efforts such as giving Hancock a new coach.

[60] Unusual for a woman at the time, Hayley also became a benefactor to the poor and contributed to numerous charitable endeavours, including providing funds to care for both veterans of the war and widows;[61] wood for the poor;[62] blankets for prisoners; and donating money to a Charlestown meeting house and to a fund financing improvements of Boston Common.

[76] Jeffrey returned briefly to London and then retired to Bath,[77] where she lived in a fashionable style in her home on Gay Street.

[78] Another reports that Patrick Jeffrey gave her an allowance while he remained in Boston living off her money like a king in the mansion of the former royal governor, Thomas Hutchinson.

[82][83] Though her story would go largely unknown, she was one of the few women engaged in trade between Britain and the American colonies, as well as the burgeoning United States.