A coronation is definitely not an event like any other one, so I guess that the choice of every detail (not only jewels, of course, but jewels too) will be purposely chosen.
In the hypothesis that Camilla would not be crowned herself, because of her marital status as regards to the Church of England's law, but would anyway attend the Coronation of her husband, I would expect Camilla (and Charles even more!) to want to counterbalance this canonical "rebuff" with a choice of jewels highlighting Camilla's regal status as consort of the reigning King. So I would expect something quite glittering, with jewels carefully selected for their regal symbolism, and not something discreet or modest. And of course, it would be out of question to have the new Queen Consort outshone by the jewels of the other princesses of the Royal Family, by the foreign female guests or by the British peeresses...
Another point: at the past coronations, British Queens have always worn "white" jewels (pearls and diamonds), and not coloured stones. This is probably a matter of tradition, and also a remanant of the white as colour of purity. Or maybe that pearls and diamonds are just considered as the "top of the top" among jewels? Anyway, I think Camilla would wear pearls and/or diamonds, but probably not rubies, emeralds or sapphires (and even less amethysts, aquamarines or topazes...).
And another detail: because of her voluminous puffing hairdo, Camilla needs large head jewels (tiaras and earrings). Smaller jewels would just sink into the mass of hair and would not be visible...
So here are my suggestions (in every subchapter opened by JasonD)!