Source: The Six Wives of Henry VIII by G.W.O. Woodward (published in 1971).
I was looking at various portraits in this little book when I noticed something. It appears Queen Mary I had combined jewels from Jane Seymour, 3rd queen of King Henry VIII.
I am sure this portrait is of Jane Seymour, although the caption did not state who she was.
But I zoomed up Jane's picture from the larger photo (it's said to be the family of Henry VIII created by van Leemput, which was copied from a life-size fresco by Holbein that was present at the palace of Whitehall which was destroyed in 1698. See the larger one, below). The people above King Henry VIII have to be Henry's parents, King Henry VII and Queen Elizabeth [formerly Elizabeth of York], therefore the younger lady has to be Henry VIII's 3rd queen (for two reasons: Jane was the only one of his wives to give birth to a living son and also in that portrait and one other portrait both ladies looked alike enough to be one same person which was Jane Seymour).
The point of posting these pictures above is Jane's "T" shaped gemstones (acting as a pendant from one strand of pearl necklace). Keep that in mind when you look at other pictures below.
This portrait (below) is of Jane Seymour. You may see that she had a double-strand-pearl choker with alternating gemstones surrounded by gold. Keep this in mind when you look at Queen Mary I's portrait further below.
Queen Mary I had this double-strand-pearl-choker with alternating gemstones surrounded by gold, with the "T" shaped gemstones acting as a pendant hanging from it.