" Her mum seems a very private person who does not court the public eye."
She has lined up an interview, pending Royal permission, with Oprah Winfrey, focusing on the racial abuse that they have been subjected to, since the start of the relationship. She has already given interviews, you must have missed them.
Doria is described as a free spirit, so, as said, she may not want to do it.
HerMajestysSecret, why do you think Megan gets to choose? Everything has to have the approval of the Queen and her advisers. There seems to be a lot of alcoholism in her family and it says a lot about her (and her Mother) that she has followed a different path. There hasn't been any airbrushing of her past, her despicable family, aren't her past, she has no power over her relatives. From the sounds of it, she couldn't trust them to stay sober and they would have the press bidding for the interviews before the Vows have been said.
My children are in the same position with their half-siblings etc. They are close to two relatives on that side, who won't accept invites because it upsets other relatives. So the relationship is conducted in private and they don't have the eyes of the World on them.