If one scrolls down to picture 4 in the link below, you will see a photo of the late QM with her daughters the present Queen and the late PM. One will also note that the QM is wearing an oval shaped diamond ring and a diamond encrusted watch. The diamond in the center of the ring looks very large.

https://www.vogue.com/slideshow/queen-elizabeth-ii-best-royal-style-moments?epik=dj0yJnU9bWg3WlN5V1htTTFFZUpUVU9PRzRPeVdJSkVpUG9jVDQmcD0wJm49MVdIa2xKVFUzbWhfNUlsNEpiS1NlUSZ0PUFBQUFBR0k0OHVz

Regards,

Dave.