Except, Amber, she did not say or imply that it was a 'totally normal thing for me to show you'. She called you out on your broken promise.
Amber, a little moral philosophy. If at the time you made the promise you had no intention of keeping it or you were recklessly indifferent to keeping it, you can also add the additional trespass of 'lying' to your broken promise.
If you uttered the promise sarcastically, then you need to work on conveying a sarcastic tone so that people do not mistake a genuine utterance from a facetiously counterfactual one, but we both know you did not mean it to be sarcastic.
And finally, if you are called out on a broken promise, do not respond unless you are willing to acknowledge or even address the failure, and do not impugn mental illness on the person calling you out.
A morally sound and emotionally intelligent adult would have said 'I did promise to do that but I have changed my mind', or 'I did promise to do that but I was mistaken about how difficult it would be for me' or 'I did say I'd do it but I was obviously kidding'. These answers might not satisfy everyone but they would be respectable.
Also in case you don't realise, you can stand in the shower in your clothes. I do that when I'm cleaning my shower. Such a photo would not violate anybody's sense of propriety, or at least it wouldn't violate it any more than any other full-length photo of you.