Having checked the diary entry, agree that song heard at a party at Lord Bruncker's. It seems that Mrs Knipp sang several songs [Pepys sang along with her, tho whether in all the songs she sang, incl this one, is not made clear], of which "her little Scotch song of Barbary Allen" was the one he enjoyed most. This suggests to me it was one she habitually sang, and this not first time he had heard her sing it [hence, surely, *her* song]; and that she had indicated it as a 'Scotch song'. The fact that she was also an actress does not appear to be that significant here, or necessarily indicate that she had learned the song as part of a play in which she was appearing or had appeared — she seemed to enjoy singing on social occasions quite independently of her profession; & indeed later in same entry Pepys sings in the coach on the way home while he feels up her breasts - so they were clearly on extremely friendly terms of which their singing together formed part. I agree however that the question is open ~ as so often in Pepys, not quite enough info to get the full picture between the lines.