I doubt very much if the first photo Janet posted is the tiara given to Mrs Greville when she married.
As far as I can see this does not match the description.
The tiara was described in one report as having three rivieres, the design being "light and graceful".
Perhaps my judgement is not universally shared, but I wouldn't be inclined to describe the jewel in Janet's image as "light and graceful". Nor do I think the style fits with the early 1890s.
Another factor is that all the reports spoke of large diamonds, some describing those in the centre as being the size of a sixpence. A sixpence was three quarters of an inch -- or just over 19mm -- in diameter. That would translate to diamonds of approximately 24 carats. I don't think that the central diamonds in the necklace in the image Janet posted are of that size.
I wonder if the image Janet posted comes from a magazine article? And that the sentence which can be partially seen has anything to do with the image above? Normally a caption to a photo would be more centred.