It is not the first time that the Queen people outside of the family are invited to the celebration at the Sandringham Estate in Norfolk. Also the parents of Catherine were such an invitation after the marriage between the duchess of Cambridge and prince William.
Meghan has a very good relationship with her mother. Doria, who shortly after the wedding of Meghan and prince Harry her job in Los Angeles opzegde, was on may 19, as the only relative of the duchess at the wedding. During that short stay in the United Kingdom would be the British royal family made a deep impression on the American. Also would they consider in the short term to move to London to be closer to her daughter to be able to live.