Much like the dispute over her date of birth, it is unclear when Gwyn began to perform professionally on the Restoration stage. It is possible that she first appeared in smaller parts during the 1664–65 season. For example, The Bodleian Manuscript of "The Siege of Urbin" has the part of Pedro (Melina- a maid servant in breeches) played by a 'Mrs. Nell'. Additionally, 'Nelle' was intended to play the small role of Paulina, a courtesan, in Killigrew's "Thomaso, or The Wanderer" in November 1664, but the play seems to have been cancelled. The use of 'Mrs' would imply that Gwyn was more likely born in 1642 than 1650 as it indicates an actress over the age of 21 (not her marital status) for which certain roles would be more suitable. Nonetheless, since players of less substantial parts are seldom mentioned in cast lists or playgoers' diaries of the period, an absolute date for Gywn's debut cannot be ascertained.