If you take away the gifted jewels that Diana received in her role as then consort to the Prince of Wales ("GJ"), Meghan could have a share of those that remained. What proportion of the remaining jewels she could potentially receive would depend on how large / valuable the collection was, or what each of the boys chose to keep for themselves as part of the legacy from their mother.
Muriel as you are clearly much better up on al this issue than I am, can I ask if you can clarfy whether the gifted jewels would have been considered diana's in the sense that she could will them to W and Harry or anyone she chose? Her Will didn't mention individual items, so we dont know for sure?
I think that if you exclude the "gifted jewels that Diana received in her role as then consort to the Prince of Wales", then what remained, however valuable or not so valuable, should be evenly divided between Will and Harry and then their wives would have access to half of the jewels. If Kate gets access to the ones in the Royal collection, that is because she is the future queen. If Meghan does not get access to the ones in the Royal collection, that's up to the queen surely?