Mary Slingsby, Lady Slingsby (née Aldridge) (fl. 1670–1685), d.1693, actress) was an English actress. After a marriage lasting 1670 to 1680 to John Lee, an actor, during which she was on the stage as Mrs. Lee, she was widowed. She then married Sir Charles Slingsby, 2nd Baronet, nephew of Sir Robert Slingsby, and performed as Lady Slingsby. Theatre historians have pointed out the difficulty in identifying her roles in the period when Elinor Leigh, wife of Anthony Leigh, was performing as Mrs. Leigh, because the homophones "Lee" and "Leigh" were not consistently spelled at the time.
In 1671 Mrs. Lee appeared at Lincoln's Inn Fields in the character of Daranthe in Edward Howard's tragi-comedy Woman's Conquest, and as Leticia in Town-Shifts, or the Suburb-Justice, attributed to Edward Revet, and licensed on 2 May 1672. Next, at Dorset Garden, where Mrs. Lee remained for ten years, she played opposite Æmilia in Joseph Arrowsmith's Reformation (1672).
In Henry VI, Part I, with the Murder of Humphrey, Duke of Gloucester, adapted by John Crowne from Shakespeare, and acted in 1681, the part of Queen Margaret was assigned to Lady Slingsby. In Henry VI, Part II, or the Misery of Civil War, from the same source, the same character went to Mrs. Lee. As the second part was written first, and probably produced first, Mrs. Lee's marriage may have been in 1681. In Nahum Tate's adaptation of King Lear Lady Slingsby was Regan, in Nat Lee's Lucius Junius Brutus, the Father of his Country, Sempronia, and Marguerite in Lee's Princess of Cleve.
After the merger of the two major acting companies in 1682, Slingsby played, at the Theatre Royal, the Queen Mother in John Dryden and Nat Lee's Duke of Guise. In Thomas D'Urfey's Commonwealth of Woman, an adaptation of John Fletcher's The Sea Voyage, produced in 1685, she was Clarinda. Her name then disappeared from the bills.