on the colour picture of the Queen Mother (with the Greville Honeycomb Tiara), the biggest of the two bracelets is not a diamond bracelet, but an emerald and diamond bracelet. The Queen Mother has regularly worn it - for instance on the following picture, taken for her 90th birthday in 1990:
The smaller bracelet (the one we are discussing from the beginning of this thread) might actually be a watch. On the following two pictures, it looks as if we can see a watch dial: