I can see why this is confusing because you see "Drottning Silvia" or "Prins Carl-Philip" (indefinite) but then it's "KronprinsessAN Victoria" and "PrinsessAN Madeleine" (definite).
From my understanding--and if anyone knows differently, feel free to correct me on this--women's titles are typically written in definite form with an ending (ex: Prinsessan Madeleine, Infantinnan Leonor, Kejsarinnan Michiko, Vicomtessan Linley, Hertiginnan Kate as some people call her).
The only exception I could find was "Drottning". That's used in indefinite form without any endings (ex: Drottning Silvia, Drottning Maxima, Drottning Rania) along with men’s titles (ex: Prins Carl Philip, Konung Abdullah, Kejsar Nikolaj)
Maybe if a Swede who understands titles can explain why this is, that’ll be awesome. It’s fascinating and I’ve never noticed it until now.