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While Mary is clearly smarter than she pretends to be, I feel like she hasn't thought this through that well. All the Albert House really has to do is voluntarily cede a part of its authority and wealth back to the royal family out of patriotic loyalty, and then relax and enjoy their status as the first and most honored among the royal vassals. An excuse would probably be needed, yes, but it doesn't have to be because the daughter of the house did something bad. It could be as easy as answering and supporting a royal centralization initiative, or in response to a bad harvest year, or because there's an external conflict somewhere, or it's just the jubilee and oh look what a perfect time to make a gesture of devotion.
I'm not even counting the rather obvious part where the future princess of the kingdom is already totally in love BFF with her, as Mary doesn't realize it herself.