The heroism & deeds of Molly Pitcher during the American Revolution are generally attributed to Mary (Ludwig) Hayes McCauley. She was born on 13 Oct 1744 in Carlisle, Cumberland County, Pennsylvania and she was the daughter of Maria Margaretha and John George Ludwig, a butcher, who emigrated from Germany with the Palatines.  Their moderate sized family also included her older brother Johann Martin. In 1769 she was employed as a servant in the Carlisle home of Gen. William Irvine. 
The first marriage is in dispute, since her mother is shown in Wikipedia as marrying John Caspar Hayes after her Ludwig husband died, and Mary marrying William Hayes, while the National Archives magazine (Teipe) indicate that Mary married a John Hayes, with no mention of a William Hayes.
Mary Ludwig or Ludwick first married on 24 July 1769 at Michael's and Zion Church, in Philadelphia, Pennsylvania to John Casper HAYS and they settled in the town of Carlisle, Cumberland County, Pennsylvania.
After his early death, she married secondly to William HAYS, a barber, who was presumably a brother to her first husband. During the American Revolutionary War, William HAYS became a gunner in Proctor's 1st Pennsylvania artillery in December 1775.  During the winter of 1777, Mary Hays joined her husband at the Continental Army's winter camp at Valley Forge, Pennsylvania. She was one of a group of women, led by Martha Washington, known as camp followers, who would wash clothes and blankets and care for sick and dying soldiers.
Continental Army records show that William HAYS was an artilleryman at the Battle of Monmouth in 1778. At that time, she carried water to the men in action and was on the field when her husband was shot down in a charge made by the British cavalry. There being no one to take charge of his piece, "Molly Pitcher", as she was familiarly called by the gunners, dropped her pitcher, stepped forward and grasped the ramrod, declaring that she would take her husband's place and avenge his death.  As her husband was carried off the battlefield, Mary Hays took his place at the cannon. For the rest of the day, in the heat of battle, Mary continued to "swab and load" the cannon using her husband's ramrod. After the battle, General Washington asked about the woman whom he had seen loading a cannon on the battlefield. For her excellent service and in commemoration of her courage,the following day he issued Mary Hays a warrant as a non-commissioned officer. Afterwards, she was known as "Sergeant Molly," a nickname that she used for the rest of her life. She served nearly eight years in the army, and was afterward placed on the list of half-pay officers. 
Following the end of the war, Mary Hays and her husband returned to Carlisle, Cumberland County, Pennsylvania. She lived at the Carlisle barracks for many years, where she washed and cooked for the soldiers and was employed as a children's nurse.  During this time, Mary gave birth to a son named Johanes (or John) Hays. In late 1786 her husband William died and some pension benefits were granted to her and her son John.
In 1793 Mary Hays married thirdly to Sgt. George John McCauley, another Revolutionary War veteran and possibly a friend of William Hays. McCauley was a stone cutter for the local Carlisle prison. However, the marriage was reportedly not a happy one. He lived on her earnings and ill-treated her. 
On 21 February 1822, the Commonwealth of Pennsylvania awarded Mary McCauley an annual pension of $40 for her service. She was granted a pension of $80 annually for life by a special act of the Pennsylvania legislature on in February 1822. 
At the approximate age of 78 Mary died on 22 January 1832 in Carlisle and was buried with military honors  at the Old Graveyard in Carlisle, under the name "Molly McCauley". 
A monument representing her in the act of loading a cannon was erected on the field of Monmouth, and in 1876 a second was erected on her grave at Carlisle. She is also represented in George W. P. Custis' painting, "The Field of Monmouth". 
Catherine Hays, m: Phillip WITTON
Samuel Hays, b: aft.1777; m: Mary GEORGE
John Ludwig Hays, b: 1783 PA; d: 20 Mar 1856 PA; m: 1796 Elizabeth REINHART
Anna Hays, b: 23 Jun 1786; d: 04 Mar 1854; m: John C. Shaffer, b: 15 Feb 1780; d: 20 Jun 1847
↑ 1.01.11.21.220.127.116.11.71.81.9 "Biographies of Notable Americans" published in Twentieth Century Biographical Dictionary of Notable Americans: volume IIV in 1904.
↑ Find A Grave: Memorial #820 for Molly Pitcher (13 Oct 1744–22 Jan 1832) buried: Old Graveyard, Carlisle, Cumberland County, Pennsylvania, USA.
Wikipedia, The Free Encyclopedia by various contributors (accessed Nov 16, 2018) for "Molly Pitcher"