If she has gained the weight during your relationship and has become increasing uncomfortable with herself, I would guess that is why she does not want sex anymore. If she doesn't feel sexy, she won't get horny. If she is going for hypnosis to help her with her weight and it actually works, she will probably return to her normal self in time.
You want her to be an adventurous nympho, well.. you have to talk to her about that. She has to feel comfortable about the things you want to do to her or have her do to you. But she will never know that you want to act out a rape scenario if you don't tell her.
