Poor Elisabeth Christine, though, would be hard to work in since she only was near the rest of the dramatis personae once a year (in Fritz' case) or not at all (the rest of them)

EC is not on my personal wishlist, but I would point out that AUs are a thing! I mean, I badly want Katte to live (honestly, I don't even care how), and all these summits never happened, so...if the author wants, say, EC to get in on the league of petticoats, more power to them. :D