The mind control was a success, she has turned into a happy, obedient pet, following every command without second thought. The gag and restraints are purely aesthetic, she won't scream unless ordered to.
That was the end of this RP session, I think I speak for both of us when I say it was lots of fun! I haven't done mind control themed roleplay before or since, but it was fun and different, and definitely something I wanna try again. Especially combined with outfitting the subject with a shiny, tight rubber uniform.