I think the diamond diadem is perfect too, except I would have her wear it with a velvet cap and turned up with ermine. It is more or less a coronet, after all. Perhaps I would have her ride to the Abbey bareheaded. Then, after the crowning itself the King returns having traded St Edwards Crown and his golden vestments for the Imperial Crown and royal purple robe, Camilla will be in the procession with him, the ermine capped diamond diadem discreetly placed on her head during the recess. I think diadem and coronet together looks awkward.
Another option is Delhi Durbar in its original upright arrangement (not flattened) worn on top of the head as Queen Mary did, Cullinans and emeralds in place along with velvet cap.
Or.......have Mary of Modena's diadem reset with real stones. Except it is probably tiny and meant for 17th century hairstyles.
--Previous Message-- : I think the diamond diadem is almost a coronet : in its own right, but diadem plus coronet : sounds like a good solution. It would : clearly identify her position. I wonder what : a princess consort coronet looks like. Was : Prince Phillip's different from the coronets : of the other royal Dukes? Would Camilla's : be the coronet she is entitled to as a : Duchess? : : Edit: I agree that she would not proceed to : a Coronation bareheaded unless she was to be : crowned. : :