Just realized this was in the "Womens Forum"...I'm not a woman, don't identify as a woman, never been a woman, ...but my wife is and we have had this issue come up.
The dive boats we have been on have been occupied with divers of all ages. We prefer small, fast boats, that usually will not have a head. I'd say that my wife and I fall about in the middle of the age average in our late 40's. I pee in my wetsuit and have no issues with that, my wife does too. They do stink after a few days, but a good rinsing with shampoo usually helps that. Our problem is with stomach issues. She has had her gallbladder removed so sometimes nature calls, actually demands, without warning and a head would be nice. The great thing about a dive boat is everybody has been subjected to the same moment at one time or another...unless they are brand new. Our dive op at our regular dive location does a surface interval at a beach club with full facilities so relief is available if you can make it to the SI.
But then, there are the other moments..... she watches what she eats for breakfast, we don't drink to excess, and generally up our pro-biotic intake in Mexico. Even taking those precautions, I have had to lose the wetsuit, drop the shorts, and take care of business. The wife has had to as well. Its a little embarrassing, but far better than shitting yourself. Usually it is met with other older divers with stories of "It happened to me when..." We have seen everything from hungover 20 somethings to 70 year old divers do the same thing. To me, its no different from people getting sick on the boat and chumming the water. It happens, its not a big deal, and as long as your not shitting on someone else...no harm, no foul. Natures call is natures call and sometimes she plays embarrassing games. Not so embarrassing that I would pass up diving because of no toilet on the boat. I promise you everyone on the boat would prefer you do a ladder check as well. It sucks...but only sucks for a moment....
I know I have seen other threads on menstral cups...but I cant help you there.
Jay