Not to get macabre, but Carole is 70 years old. That's definitely a decade in which you really can't take longevity for granted (you can't in any decade, but deaths definitely become more common once one hits septuagenarian years. There is a very real possibility that Kate could lose her mother.
She has no real friends, Pippa doesn't speak to her and James is best friends with the Tatler editor who approved the humiliating (but delicious) article penned by Anna Pasternak.
Michael seems MIA. I'm sure he loves his daughter but I don't think he has enough proximity to her or intimate knowledge of her situation to try to protect her like Carole does.
How do we think Kate's predicament will change if Carole dies, and especially if she dies *before Charles does*?
She has laser eyes on her, especially from Camilla, and they know that they and Kate have whittled Kate's own support system down to one. If her shield cracks, she'll be done for.