Which shot do they refer to?
For real Meghan Markle is the same as Lady Diana? According to some experts of the English royal family there would be some similarities in the behaviors of the two women, in some shots compared. For those, on the other hand, who do not look favorably on Prince Harry’s wife, these are poses studied at the table or in any case attitudes common to all mothers.

To make this comparison, you have to go back to the Christmas card that i Dukes of Sussex they also spread on the internet. Prince Harry is seen holding little Archie in his arms, looking down, while his father looks at his women laughing.
Meghan Markle leans on her husband’s shoulder, who is also sitting and smiling, admiring the little girl Lilibet Diana laughing heartily in her white dress. A shot that closely resembles that of Lady Diana holding little William in her arms.
Some experts from the English royal family and even body language experts have identified this couple’s Christmas card many similarities between the way the former actress holds little Lilibet and how Diana held her son Harry in 1983, in a very famous shot.
The Christmas snapshot is the first to officially show the newcomer to Harry and Meghan’s family, who after Archie’s birth also welcomed little Lilibet Diana (not asking the Queen first if she would like her nickname to be used, with which I’m few to call her).

Meghan Markle equal to Lady Diana? There are those who see the similarities in “being a mother”
Judi James pointed out that Meghan Markle’s body language, like Lady Diana’s, is that of a loving and caring mom:

Both Meghan and Diana are in profile with their heads tilted back to watch their children as they lift them into the air and on both faces there is a joy that is reflected in the faces of the children.