I fully sympathesise with the OP: it's clear that the OP was both embarassed and quite rightly upset, and it's also clear that the CC was at fault on this occasion.
The OP has already said hindsight is a wonderful thing...and it is. But life's mishaps are also great learning opportunities. No lasting harm was done, except to some clothes! So, in the grand scheme of things, I would chalk this up to experience.
I don't want to stir the pot too much, given OP has agreed they have may have replayed the tape differently. Very understandably, a beach holiday in Rio might have seemed the perfect tonic to escape what must have been a very upsetting diagnosis, and I hope in many ways, the holiday is proving to be so in many more ways. But knowing how to navigate a new chronic illness, days after diagnosis, is rather different to living with it day to day. It's not about "fit to fly", or the disabilities equalities act. An accident may have happened (and may happen again, on the return trip, or in 6 months' time, or never) even if everything had otherwise been in place and the CC had behaved differently.
I also agree with some of the posters that I don't think class of travel will that be critical an issue for the return journey: being in J is not really risk mitigation of soiling accidents in my (professional) opinion. The OP may have been (not saying they absolutely were, but if so, it's understandable) shy about insisting on using the toilet, because they hadn't experienced the accidents that may ensue before...but now they have, and hopefully with it, found a confident voice to help them navigate future scenarios.
Wishing the OP good health for the future.
tb