Princess Grace wore the VC&A Tiara only once, at Princess Caroline's pre-wedding ball. There aren't even good pics of Grace wearing it, just one blurry wide shot.
Yet the tiara has become closely associated with the Princess, because VC&A is constantly exhibiting it, stressing that it had been "worn" by the Princess. They never say that she had "owned" it.
Later the VC&A tiara was also worn by the late Countess of Paris at a photo shoot for a Magazine.
I believe that the tiara was owned by the jewellery house and Grace loaned it. She has worn several other loaned tiaras by the way.