Suggestions for the identity of the sitter in this portrait have included Lady Margaret Douglas (1515-1578) and Margaret Howard, Lady Arundell, the sister of Queen Katherine Howard, based on provenance.
The portrait was first recorded by George Vertue in 1733 when at Sutton Place, Surrey, the seat of the Weston family as 'a Lady at len. in black. manner Holbein'.
The fashions of Lady Jane Grey's youth. Notice the squared brim of the French hood and the raised neckline with ruffles.
*Both J. Stephan Edwards and Lee Porritt (The Beaufort Miniature Portrait – Lady Jane Grey Revisited) dates the Fitzwilliam Portrait to the middle of the 1550's, due to the flat crown of the French hood and the standing collar of the outer partlet (the black velvet piece across her shoulders, tied under the arms), which strongly indicate the mid-1550's, and the frill seen at the neck which by the mid-1550's had grown in size and had begun to surround the face.
(For my identification of the sitter in this painting as Katherine Brydges, Lady Dudley, please see my The Fitzwilliam Portrait page. Reasons for identification: The lady in the Fitzwilliam Portrait is also portrayed in a miniature by Levina Teerlinc from around 1560 now in the Victoria and Albert Museum. Katherine Brydges, Lady Dudley was a lady-in-waiting to both Mary I Tudor and Elizabeth I Tudor, and would therefore have been in the perfect position to be an object of portraits done by court painters Hans Eworth and Levina Teerlinc. Furthermore, she was born in c.1524, being in her early thirties when the Fitzwilliam Portrait was painted, and in perfect keeping with the age of the lady in the portrait. She was married in either late 1555 or early 1556 to Edward Sutton, 4th Baron Dudley, in a match encouraged by Queen Mary, making it likely that this was a wedding portrait, as that date matches perfectly with the assessment of both J. Stephan Edwards and Lee Porritt that this portrait dates to the middle of the 1550's. Lastly, the embroidery of the lady's collar has a pattern that can be found again on other members of the Brydges family. It is probably a stylised version of a bridge, a play on the family name of Bridges. There is also the matter of the girdle prayer book the lady is holding in the portrait. It is decorated with what appears to be a D. Which would correspond with her new married name of Dudley. Two years previously Lady Jane Grey Dudley, daughter of the Marquess of Dorset had left her beloved girdle prayer book to Sir John Brydges, Lieutenant of the Tower of London. He was Katherine's father.)
Bess of Hardwick
Mary I Tudor (18 February 1516 – 17 November 1558)
(For my identification of the sitter in this painting as Amy Robsart Dudley, please see my The Yale Miniature page. Reasons for identification: The lady in the Beaufort Miniature is the same one as the lady in the Yale Miniature. I have always found the arguments that the lady in the Yale Miniature is Amy Robsart persuasive.)
Katherine de Vere, Baroness Windsor (1542/1543 – January 17 1600)
I have dated this painting to 1572 based on the collar. It is identical to the one worn by Walter Devereux (1539–1576), 1st Earl of Essex in the portrait inscribed 1572 above. For my identification of the sitter as Dorothy Petre Wadham see our For Reference page and our The Pagets page. The Royal Collection points to another portrait which appears to represent the same woman at Petworth, with another version of the portrait at Petworth belonging to the Duke of Sutherland. The copy shown above owned by the Duke of Sutherland was sold by Christie's in 1972. It is inscribed with the date 1560 and the sitter's age, 24, meaning that she was born in either 1535 or 1536. This precludes Frances Brandon, whom the portrait in the Royal Collection has often been associated with. She was born in 1517. Petworth is the home of the Egremonts, and searching through their female ancestors, I came over Dorothy Petre Wadham. She is not a direct ancestress, as she and her husband did not have any children. However, the Egremonts are direct descendants of one of her husband's sisters, and were his eventual heirs. There is still another, fully authenticated portrait of her at Petworth, still belonging to the Egremonts. She had many portraits of herself painted, and we know, from these fully authenticated portraits that she was born in either 1534 or 1535. This matches precisely with the birth year of the sitter in the other portrait. Furthermore, there is a clear resemblance between the striking features of the lady in the portraits and the features of Dorothy Petre Wadham in her authenticated portraits.
Mary Kytson, Lady Darcy of Chiche, later Lady Rivers (1566 – 28 June 1644)
(For my identification of the sitter in this painting as Dorothy Wadham (née Petre), please see the discussion of this portrait on my For Reference page, and I believe I have conclusively identified the sitter on my The Pagets page.)
Agnes Keith, Countess of Moray (c. 1540 – 16 July 1588)
Agnes Keith, Countess of Moray
Margaret Audley, Duchess of Norfolk (1540 – 9 January 1564)
 That must be this portrait: «Indeed, despite her own affinity for things Spanish, Mary was herself depicted wearing a much narrower – and notably free-form and unstarched – Spanish-style ruff only once.2 She more commonly wore the standing-collared partlet seen in so many of the other portraits included in this study. Even in portraits that depict Mary wearing a chemise under her partlet, the collar usually has a loosely flowing and unstarched simple ruffle.» (J. Stephan Edwards, A Queen of a New Invention, p.114) «2Queen Mary I, Hans Eworth, 1557, oil on wood panel, 8 x 6 1/2 in., private collection.» (J. Stephan Edwards, A Queen of a New Invention, p.115)
This portrait is almost (but not quite) identical. Mary is dressed in the same outfit, however, and this portrait too is dated to 1557.
This excellent overview over the portraits of Hans Eworth dates both portraits to 1557. It has this portrait as being 8 x 6 ½ inches, while the one that we only have a black and white photograph of as being 9 ⅞ x 7 ½ inches, so it appears to be this portrait J. Stephan Edwards meant.
 Hope Walker and Kate Emerson suggest that sitter in Unknown Lady, Formerly Lady Anne Penruddocke may in fact be Anne Wootton alias Woodhouse alias Reppes, Mrs. Bassingbourne Gawdy:
ANNE WOTTON (1536 – June 1588)
Anne Wotton was the only daughter and heir of John Wotton (Wooten/Wootton) of North Tudenham, Norfolk (d. 14 November 1545) and Elizabeth Bardwell and the granddaughter of the John Wotton who, sometime after 1541, married Mary Neville, Lady Dacre as her second husband. In 1545, Anne’s wardship was held by John Millicent, who sold it to Sir Anthony Rouse. In 1547, Rouse sold it to William Woodhouse. In 1554, Anne married Sir Thomas Woodhouse of Waxham (1535–1556). In 1557, she married Henry Reppes or Repps of Mendham, Suffolk (1509 – 10 February 1558). Both marriages were childless. On 25 September 1558 she married Bassingborne Gawdy of West Harling, Norfolk (1534 – 20 January 1589/90). Their children were Bassingborne (19 May 1560 – 3 May 1606) and Philip (13 July 1562 – 27 May 1617). Portraits: Hans Eworth, who painted two portraits of Lady Neville, is also said to have painted portraits of Anne and her third husband (now lost); Anne Wotton may be the subject of the portrait called “Lady Anne Penruddocke” which gives the age of the sitter as 20 in 1557.
«1557 BASSINGBORNE GAWDY and ANNE WOOTTON his wife.
Vertue (Brit. Mus. Add. MS. 23070, fo. 75) notes: 'Amongst old paintings at Bow left by Mr. Le Neve Norroy at his house there. Bassingborne Gawdy Esq. on board, small life, ætatis 22. The mark of the painter HE. 1557 ... his wife ætat 20. HE. the mark of the Painter also. These two pictures, as they are not half so big as the life, are drawn with a pretty good spirit and firm manner, the colouring faded.'
Bassingborne Gawdy of Mendham, Norfolk, son of Thomas Gawdy of Redenhall, Norfolk, Serjeant-at-law, and Anne Bassingborne his wife, married in 1558 Anne, daughter of John Wootton of Tudenham and Elizabeth Bardwell his wife, and grand-daughter of John Wootton of Tudenham, whose second wife was Mary Nevill, Baroness Dacre (see above). Anne Wootton had been previously married, first to Thomas Wodehouse, and secondly to Henry Repps.»
That does seem to be a very good match with portrait of an Unknown Lady, Formerly Lady Anne Penruddocke.