Okay, I think I found a way for the Duchess to win the trial or if nothing else put a big kink into the Sperado's defense and its pretty obvious. Its the middle name! Leslie doesn't have a 'blessed' middle name which is deem very important for noble when they have children! I bet the church keeps records of that stuff that could be used to show proof!
Oooh this is really interesting! I'm curious as to her reasoning of transforming her brother into a rabbit. If I were a betting gal, my guess is that she wants him to experience the feeling of being hunted and running away from a scary adversary, i.e the same feeling girls feel when someone is stalking them!