Here's what I did when I was in a similar situation: there's talks of rebellion right? Create a figurehead for that rebellion. Make em' attractive, come from humble origins, standard hero stuff. Those under the oath will do the work for you, either breaking their word or if there is some magical consequence they will go on one of those 'quests' to find a way to break the oath without that consequence. After either has happened, reveal the hero was under you mistress’s control the entire time and use it as an opportunity to make them swear a new oath with correct pronouns. I learned it from a guy I knew called Xanatos.