Is this (formally) a portrait of a living person (as opposed to a painting of some historical or genre scene that Peg Hughes happened to model for Lely) and if so what are the social parameters of breast-baring in 17thc female portraiture? Would it be usual for a genteel lady to be painted with a nipple showing? If not (or if so) does it carry some meaning about the sitter's status e.g. as married/unmarried, mother, virgin, mistress, prostitute, bluestocking, actress?Of course, I'm not the person to ask, since I've always regretted not having studied art history on anything like a formal basis – but my own viewing of Restoration portraiture of women suggests, as Catherine MacLeod writes, that "While in practice there is almost never any distinction between the poses Lely used to portray 'virtuous' women and those with more dubious reputations, portraits that include bare breasts seem exclusively to depict mistresses." (See this lively review of a 2003 exhibition of Restoration portraits of women.)
The graceful Lely portrait of Diana Kirke (left) was reputed banned from the London Underground on the grounds that the exposure of her left nipple might be "distracting" to commuters. Kirke had a 13-year liaison with Aubrey de Vere, Earl of Oxford, & the Yale art historians speculate "It is likely that her lover commissioned the portrait for his private apartments, where it would be seen and admired only by his inner circle of friends." (The Kirke portrait was replaced on the Tube by an equally lovely but more discreet portrait of the Duchess of Richmond.)
Of all of the women painted by Lely, the only one I know of to appear in full undress is of course Nell Gwyn, another actress & the most famous of Charles II's mistresses. (And a woman of considerable spunk: when an angry mob assaulted her carriage, believing it contained a less popular – and Catholic – paramour of Charles's, she said, "Pray good people, be civil; I am the Protestant whore.") Samuel Pepys reputedly kept an engraving of Peter Cross's portrait of Gwyn as Cupid (right) over his desk at the Admiralty.
As to whether their clothes "fit," I suppose they fit as well (or badly) as those of my own undergraduates; and whether something gets exposed (as with my own undergraduates) is a matter of a delicate semiotic – a rather different semiotic, d.g., now than then.