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) «2 Queen 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)
Dickinson Private Advisors & Fine Art Dealers does specify that the portrait is oil on panel, measuring 22 x 17.3 cm. (8⅝ x 6¾ in.).
This is almost exactly the exact measurements mentioned by J. Stephan Edwards, but not quite.
Another possibility is that J. Stephan Edwards is referring to the portrait in footnote 2.
These two portraits are almost (but not quite) identical. Mary is dressed in the same outfit, however, and this portrait too is dated to 1557.
 Of Crymsen Tissue: The Construction of a Queen. Identity, Legitimacy and the Wardrobe of Mary Tudor
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.
Anne Wotton – A Who's Who of Tudor Women
Hope Walker suggests this in Hans Eworth Catalogue Raisonné: Catalogue Overview – Monogrammed & Documented Works.
In the article The Painter HE (‘ Hans Eworth.’) by Lionel Cust in the Second Annual Volume of the Walpole Society the following description is given of two portraits of Bassingbourne Gawdy and his wife:
«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.
 See On the Portrait of ‘Lady Anne Pendruddocke’ in a Private London Collection, Compiled by Hope Walker, MPhil/PhD Candidate | The Courtauld Institute of Art