I know neither you nor I know Doria personally, so ultimately we’re both speculating, but I actually have the complete opposite view to you about Doria having had a “tough time”.
She married a man who was financially secure, so didn’t need to work. And according to Bower’s account, Doria regularly smoked weed at home, and Samantha suggested that her father knew Doria was sleeping with other men.
Doria apparently was not being particularly affectionate towards the older Markle children, who were already dealing with being abandoned by the mother, a workaholic father and the upheaval of having a new stepmother.
Then the arrival of a new baby, Meghan, who was apparently treated as the special little princess who received all the loving attention and was even sent to private school.
I don’t think the two older Markle children are awful at all. If Bower’s account is accurate, I think they had a pretty shit start in life and, from their perspective, a stepmother who didn’t seem particularly fond of them, while their younger half-sister received very different treatment.
But like I say! Who knows the truth, neither of us know them! (Thank god)