If Doria goes to Sandringham (I doubt it), there’s no way she’ll celebrate it with royals, last year Harry had to take Meghan to Anmer Hall and she only got the church walk with royals. Non-royals or royals’ mothers (aka Fergie) don’t get the royal treatment, the most they can get is staying at a nearby cottage and maybe a Christmas dinner. No gifts exchange, no drinks after dinner, no church walks, they’re alone for the most of the time.