ETA - perhaps not totally Ehell approved, but it is a sound to be expected in public facilities. Also, desperate situations call for desperate measures.
Certainly not ehell approved, but if I were disabled and needed to use that stall, I would have squeezed myself into the stall
with her and used the darned toilet. If she got in my way, well, some urine might not make it into the toilet.

I would have given her warning first. When she said, "I am going to be a while and if you wait - I'll just be longer!" I would have firmly said, "I have
no choice; I must use this stall right now.
You can use another stall." I would not have left unless it was to get security to have her sorry butt hauled out of the handicap accessible stall.
BTW - My husband is disabled. He needs the handicap accessible stall. If some guy tried pulling that on DH, he would have whipped it out and peed
on the jerk if he didn't move out of the way fast enough. DH is not a patient man and he doesn't tolerate SSs.