I think that this is the tiara she was photographed wearing at the 1902 Coronation. Initially, I thought there were two different tiaras but, when I took into account the angle of the coronation photo, I came to the conclusion that it is the same tiara. What do others think? I know I could be very wrong.
For the Dowager Countess to be able to donate this tiara, it had to be a personally owned item, not an entailed family jewel.