It feels a little goofy to go through Alphonso suspecting something + being methodical about it and an investigation being mentioned, to just end up with "actually I can just understand your catspeak, haha". I guess it streamlines the story a bit, though.
I assume she'll transform back when she hears the duke mention loving Marie, or something. Then it'll be awkward as she poofs back into a human without any clothes right next to him.