The source of the excrutiating pain was Prudencia's bladder, which felt like it was about to burst into a mass of flesh.
Prudencia had to go pee.
Just as had been described, the pain in her abdomen was so incredibly hard that she could do little but stand there with her legs crossed, doubled over. But she knew that she had only two choices. Either wet herself right there and then under the clan surveylance cameras, or somehow try to get to the bathroom she had encountered during the mission.
Eventually she got to the lavaratory whimpering from the pain which was getting worse and worse.