“i can’t in good conscience ask her to make good on that promise can I?”
Of course you can. otherwise she simply should not have made the promise. She is trying to gatekeep your sexuality and being allowed to do so has consequences, namely keeping the promise.
Unless this is some sort of dominance kink that you are BOTH into, it’s nowhere near healthy.
It’s YOUR body. Wank away.
She can’t keep you from doing what you want or need. Honestly, this sounds very controlling and you should tell her how you feel.