"Primarily a singer and dancer, Mrs. Knep developed into a first-rate actress." She began her career with the King's Company under the management of Thomas Killigrew. She made her debut in the title role of Jonson's Epicene on 1 June 1664. (She was cast as Lucetta in Killigrew's 1664 planned production of his Thomaso, with an all-female cast, which was cancelled before completion.) Knep played major and minor roles in a range of productions of the 1660s and 1670s, including:
- the Widow in Beaumont and Fletcher's The Scornful Lady, 1666
- Guiomar in Fletcher and Massinger's The Custom of the Country, 1667
- Alibech in Dryden's The Indian Emperour, the 1667 revival
- Asteria in Dryden's The Maiden Queen, 1667
- Beatrix in Dryden's An Evening's Love, 1668
- Aminta in Fletcher and Massinger's The Sea Voyage, 1668
- Nakar and Felicia in Dryden's Tyrannick Love, 1669
- Ladt Flippant in Wycherly's Love in a Wood, 1671
- Hyppolita in Dryden's The Assignation, 1672
- Lady Fidget in Wycherly's The Country Wife, 1675
- Eliza in Wycherly's The Plain Dealer, 1676
- Mrs. Dorothy in d'Urfey's Trick for Trick, 1678 — her last known role.
In addition to playing these and other parts, Knep also sang and danced in plays and spoke Prologues and Epilogues. She never achieved the same fame as her younger contemporary Nell Gwyn; Knep had the lead female role in The Assignation — but the play was a flop.
"Mrs. Knep was the wife of a Smithfield horsedealer, and the mistress of Pepys" — or at least "she granted him a share of her favours." Scholars disagree on the full extent of the Pepys/Knep relationship; but much of what later generations have known about Knep comes from Samuel Pepys' famous Diary. Pepys first met Knep on 6 December 1665; he described her as "pretty enough, but the most excellent, mad-humoured thing, and sings the noblest that I ever heard in my life." He called her husband "an ill, melancholy, jealous-looking fellow" and suspected him of abusing his wife. Knep provided Pepys with backstage access, and was a conduit for theatrical and social gossip. When they wrote notes to each other, Pepys signed himself "Dapper Dickey," while Knep was "Barbary Allen" (that popular song was an item in her musical repertory).
Mrs. Knep had at least one child, a son born in June 1666. She may have been a mistress of Sir Charles Sedley. In the late 1670s she became the mistress of actor Joseph Haines; Knep died in childbirth in 1681.
- John Harold Wilson, All the King's Ladies: Actresses of the Restoration, Chicago, University of Chicago Press, 1958. 
- Wilson, p. 154.
- Peter Cunningham, The Story of Nell Gwyn, Gordon Goodwin, ed., Edinburgh, John Grant, 1908; pp. 12, 171.
- Pepys' Diary entry of 8 December 1665.
- John Downes, Roscius Anglicanus, London, 1708; Montague Summers, ed., London, Fortune Press [no date]; reprinted New York, Benjamin Blom, 1963; p. 93.