Wait. I just went back and watched all the scenes from The Miller’s Daughter that have Princess Ava in them. It is pretty clear that she was there to hopefully marry Prince Henry and join their two kingdoms together. If that is the case the scenes with Cora, Leo, and Ava can’t be before the Miller’s daughter because Ava wasn’t married during the Miller’s a Daughter.
So that means that Cora really is royalty at that point and is married to Prince Henry.