Queen Louise of Prussia really disliked Napoleon. Her influence was important for the Prussian declaration of war in 1806. Remove her and differently balanced court politics might avoid the Fourth Coalition War. No humiliating defeat for Prussia's army; no loss of half the territory.
Instead, Prussia gobbles up Hanover as gift from Napoleon, and when Austria fights and loses against France in c.1809, Prussia gets Austrian West and Old Galicia. Who knows, apparently Napoleon even offered the title of "Emperor of North Germany" to Friedrich Wilhelm.
Basically, Prussia is now a Saxony on steroids, with a untested and unreformed army and lots of enmity among other powers, diplomatically wholly dependent on Napoleons goodwill. When (not if) he goes down, so do they. Perhaps Russia's influence will keep a rump Prussia alive as its vassal.
But they will probably lose/never gain the potential industries of the Ruhr in the West and Upper Silesia in the East.
Prussia proper, Pomerania and Brandenburg will make them utterly dominated by the archconservative, anti-urban agrarian Junkers. No influience by those upstart bourgeois capitalists!