There are many 'apparently's and 'implied's in that story. Dimitri is not the sharpest sword in the armory, I would not be surprised if he misinterpreted something. He and Edelgard are both very emotional. There is also the possibility that Edelgard believes she is responsible when she is not - I am not certain how much of Edelgard's childhood memory should be taken at face value. If Adrestia were responsible, it would be at the behest of either Duke Aegir, Lord Arundel - or the thing wearing his skin I do not recall precisely when his mannerisms changed - and Lady Patricia, or my father.

I only know that it would not have been in Edelgard's personal ability to perpetuate. Nor Hubert's. I make no claim as to desire or moral willingness - only practical limitations.