Charlie-
We raced dinghy sailboats (18 feet and under for the non-sailors) for 33 years in San Francisco Bay and the rest of California.
I suggested the Lady Jane approach to one of the gals who used to race with us who was complaining about the ladies inconveniences, and I thought she was going to get one and shove it down my throat (or somewhere else)! Didn't help that she was a Dyke.
The preferred relief method when wearing a full length wet suit in the Bay for gals was to jump overboard in the 57 degree water, pee in your wetsuit, slosh around a bit of water, then get back into the boat and race. Ashore later, a water hose down the front of your westsuit did a nice rinse until peeling it off later in the clubhouse shower. (Men could use the zippers in the front of their wetsuits.)
See if she likes the wetsuit idea. It's probably cheaper than an Airhead Composting Toilet or an open air bidet on the swimstep.
As they say, "Got to Go!"
Joe.