I know it really isn't the same, but...
I cared for my Mom for the last 5 years of her life. Her Vascular Dementia (stroke-related) would often cause "catastrophic reactions" to things that we took for common. One night, she became afraid of her poop.
I will spare you the details, but it was horrifying. Not just the logistics of the clean-up (which still haunt me to this day) but just to see someone so afraid to poop, of her poop, of what was happening as she pooped.
Luckily, we recognized the catastrophic reaction for what it was, and so we could deal with it appropriately. She was, oddly enough, able to control her urine and hold her bladder until fairly near the end, but she lost control of her bowels very suddenly and spectacularly, and never regained control.
After that night, we created potty routines that helped to prevent any further meltdowns. Some of the things we did were:
- When she had to transition to adult pull-up diaper panties, we called them "hospital panties" because the first time she wore a pair was at the ER one night. We never referred to them as anything like a diaper.
- (Re-)Taught her to sit on the toilet, and to (while seating) reach with her hands towards her toes (so that she was "doubled over"). This enabled me better access to clean her.
- Kept plenty of wipes, plastic bags, gloves - all the supplies needed - organized right next to the toilet so that one person could help her and didn't have to call for help because something needed was missing.
- When she arrived at the point where sitting on the toilet was just to clean her up and help her change into a new pair of hospital panties, we continued to treat it just as if she was going in the toilet. There was nothing to be gained by behaving any other way, so...
- Gave her a bright, clean bandana to play with in her hands every time - it kept her distracted, and kept her hands out of the toilet. I kept a basket of clean, laundered bandanas next to the toilet with the other supplies. When the bandanas were no longer effective, we tried different things: pieces of ribbon, small "Happy Meal" toys, sponge balls, anything that would hold her interest.
- We made up a "poopy song" that we sang every.single.time she went to the bathroom. As time progressed, she could no longer sing it, but we sang it anyway as part of the routine.
- We made a point to always use the same products, the same procedure, the same steps every time she toileted. If we were going to be away from the house, I had a "go" bag (pun intended!) that was stocked with products that we took with us (yes, like a diaper bag)
Obviously, a lot of these things won't apply to the OP, but if her little person could learn to sit on the potty, and then bend forward to make cleanup easier, this might make using the larger handicap stalls and companion restrooms much easier. I wouldn't want to have to lay any member of my family on the bathroom floor anywhere, and I understand the logistics of trying to clean/change someone in unfamiliar territory.