I have no idea what Andrew Morton said; I didn’t get it from him.
He just says that Diana felt that the spirit of her grandmother was looking after her. That may be occult and new age and shocking and bizarre to a secular and cynical British journalist, but it's not terribly different from what a lot of Americans who claim to be Christians believe.
Of course it may be that Diana believed her dead grandmother actually was creaking the floorboards and rattling the cupboards or that she tried to get in touch with her through a seance, but that's not the only explanation.
It's said that Diana did believe in and consult psychics and astrologers. But there's been so much rumor and disinformation that it's hard to know what to believe. I'd just point out that some people may be condemning her for believing something very close to what they themselves believe.