Her contralto pitch and relatively heavy build suited her for breeches roles, and she played the title role in Arne's Artaxerxes on 25 January 1777, Belford in Thomas Hull's Love Finds the Way, Colin in Charles Dibdin's Rose and Colin, and most notably Captain Macheath in John Gay's The Beggar's Opera where in 1777 she was the first person to sing "A-Hunting We Will Go", a song written by Arne for that performance.

[4] Her debut performance in The Beggar's Opera was greeted by protests because a woman was playing the role of a lead character.

[3] After 1779, Kennedy performed as Young Meadows in Love in a Village and Don Carlos in Richard Brinsley Sheridan's The Duenna.

While there, she performed in many roles, including Don Alfonso in Thomas Arnold's The Castle of Andalusia, Patrick in John O'Keeffe's The Poor Soldier and Mrs Casey in his Fontainebleau, Margaret and then Allen-a-Dale in William Shield's Robin Hood, as well as parts in Shield's Rosina and Omai, and also in Henry Fielding's Tom Thumb, William Kenrick's Lady of the Manor, and Dibdin's The Islanders.

[1][3] She retired from public performance in 1789, appearing for the last time on the theatre stage in the role of William in Shield's Rosina on 2 April 1789.