Greetings,
I beg your indulgence if I am perhaps too bold for what I am about to suggest, but having perused those offerred sofar, I percieve them to be rather mundane, all in the 'straight & narrow' of the BDSM community 'norms'. And yes I do use the word 'norms' guardedly. But to the concept ;
Having read that sophie is 'sensitive' regarding her smallish breasts, I offer what simply would be the most dire punishment one could inflkict upon her, perhaps too severe even to be contemplated,
Compel her to dress as a Man, strapping down what little titmeat she has so as to make it vanish altogether, not only that but to function as a man, into a gay bar and to 'service' the customers of that establishment, orally & anally only never revealing that she is in fact female.
The needed precautions for health reasons I am sure you know and will not bore you with, yet if I have correctly perceived your description of this submissive then this indeed would be the ultimate humiliation of her : nothing less than the complete and total repudiation of her existence as a female.
Respectfully,
Sir Draconis :[