She is indeed very discreet in the choice of jewels and not for lack of money, just a way of being.
Another case of a very discreet Queen, never bejeweled even if she would have the necessary jewels, is Queen Sofia of Spain, a favorite of mine. Despite having several important diamond collets necklaces (i.e. Queen Victoria Eugenia's long sautoir of diamonds), two sets of turquoises and diamonds jewels (one especially impressive), important sets of sapphires and diamonds, rubies and diamonds, twin brooches of carved emeralds and diamonds with matching bracelet and earrings, despite all this, she wears pearls most of the time, or very tiny diamonds necklaces. I forgot to mention a 'V' shaped necklace, part of a ruby set that she very seldom wears, which it includes also an important bracelet and watch.. Here it is: