I want the designer to have creative freedom. With that said, I do have some ideas and have included some book covers for "look". It needs to be a rich look representing royalty but with an ominous tone evident somehow.
#1 Idea- Collage effect (example book cover attached) in background containing subtitle elements such as prison cell, prison door, keys, letters, etc. (browns, purples, golds, black, etc). White letter on top would have title, subtitle, author.
#2 Idea-Elegant, kingly look in purples, grays, blacks and white. A gold key lying on top of a stack of king's letters. Light shining in through cell window. Purple or gray background
#3 Idea-Book cover wrapped in white seamless unintelligible letter. Gold key(s) lie on top with sun streaming over both through the cell window. Barred window shadow is subtle but evidence of her captivity.
Including a person or shadow of a person in a cover design is OK but I haven't thought much about how that should look. Would need to be a slender, tall blonde with kingly attire.