A senior royal source said the unique move was "a very thoughtful gesture".
The offer is without precedent, even to the in-laws of Prince William.
Although the Queen has asked members of the Middleton family to join them for the Christmas morning service, they were close to Kate and William, Annes Hall, and not to Norfolk Estate.
The source added, "It is a sign of the Queen's respect for Meghan and a recognition that she has no other relationship in this country – unlike Kate, who has the support of a very close family."
It is also a heartfelt move towards Doria Ragland, 62, who impressed the Queen with her calm composure at Prince Harry's May wedding, whose dignity, in the face of worldwide media interest, was in stark contrast to the mischief of Meghan's father, Thomas.
Her presence in Sandringham will speculate that Doria, who lives in Windsor Hills, Los Angeles, is considering a longer stay in the UK to support her daughter before Meghan is born in the spring.
Doria may have already started preparing for her departure from Los Angeles by giving up her job as a social worker at Didi Hirsch's psychiatric care clinic in LA.
She also worked as a part-time make-up artist, travel agency and yoga teacher.