I think a PC could wear the Koh-i-Noor as a brooch, in its lozenge setting.
For going to the Abbey, the PC could wear the Vladimir tiara with diamond drops! Wow! This would introduce something unqiue for the unusual circumstances in over a century.
At the point of crowning the King, the PC could add her coronet just like the peers and peeresses do. Two head items are common at a coronation so I see no problem with those two worn together.
Both would be worn by the PC on leaving the Abbey and in official photos.
I believe the coronet worn by Phince Philip was specific for a prince consort. I have no idea what the coronet for a princess consort would be but expect it would be a smaller lady's verson of his. I hope someone can advise here.