I was delighted when almost eight years ago I read the suggestion that this young lady might be Amy Robsart. Eric Ives had just published his marvellous book on Lady Jane Grey and mentioned this idea in a footnote. The reason was that David Starkey had recently proposed that the c.1550 miniature was a portrait of Lady Jane Grey, painted during her imprisonment in the Tower. There were issues with the sitter’s age, though, which according to the inscription was 18 or in her 18th year, and Jane was definitively dead by then.
Furthermore, the sitter, according to Eric Ives, ‟wears a gold brooch mounted with a black classical head and behind it a bunch of acorns and a spray of yellow flowers”. The flowers were identified as, possibly, gillyflowers or cowslips, the former arguably pointing to Guildford. The acorns, however, could point to a connection with Robert Dudley. His name reminded educated people of robur, Latin for oak. And we know that Robert Dudley actually used the oak symbolism in his youth: One of the carvings in the Beauchamp Tower has an oak tree and the initials R D, and the more elaborate Dudley carving commissioned or carved by his brother, John, Earl of Warwick, also uses acorns and oak leaves.
The theory was that the miniature might be a portrait made to commemorate the wedding of Amy Robsart and Robert Dudley on 4 June 1550. Born on 7 June 1532, Amy was almost exactly 18 years at the time.
If this picture is really Amy Robsart, then isn’t it likely that Robert Dudley would have kept the picture after her death? Many inventories of Robert’s collections, of paintings and beautiful artefacts, survive, more than of any other Elizabethan, alas this miniature seems not to be among the items listed and described.
Many other theories as to who this lady may have been have been proposed: That she was Elizabeth I as princess, Katherine Howard, Lady Jane Grey, or even Mary I as princess. Only the Robsart theory, though, answers the question why she should wear acorns around her jewel.
After so much time, I’d still like to think it’s Amy, although I am not sure I really care any longer … One has to consider that the case rests only on a few acorns and oak leaves and the fact that the sitter is about 18 years old. How common were such pictures? How many people would have commissioned such things?
See also:
Elizabeth, Jane, Amy? The Riddle of the Yale Miniature
All Things Robert Dudley 
It’s very unlikely to be Mary I unless it was painted well after the fact; at eighteen she was in the middle of her three years of confinement/imprisonment at Hatfield House, and the image doesn’t resemble her any more than it does Elizabeth I.
Could this be a picture of Lettice Knollys commemorating her wedding to Dudley? We know Elizabeth engaged in, for a lack of a better term, photoshopping, as she aged. I think that Lettice was brash enough to have had the miniature and hidden it away, especially if she was trying to spare herself the wrath of Gloriana! Reportedly, Lettice and Elizabeth looked very similar and were cousins. So on a circumstantial level it could be a picture of a young She Wolf.
Very difficult to believe that Jane’s portrait would have been commissioned during her imprisonment in the tower to be honest, even if the prospect of her sentence being carried out was very low at this point.
As for her age, based on current evidence, J. Stephan Edwards hypothesises that Jane was born in late 1536, so she would have been in her eighteenth year during 1554, but again, highly unlikely that a portrait would have been commissioned of her in January 1554.