After Vivienne's diarrhea had finally passed, I started to worry that she had a urinary tract infection. She started crying when I took her out of the bath tub and was clearly indicating to me that the pain was coming from "down under." The next day, I called the advice nurse, who recommended that I go ahead and bring her in, just in case. So we all packed up and were at the doctor's office about 20 minutes later.
At the pediatrician's office, they stuck a little bag to her with adhesive. The purpose of the bag was to collect her urine. It hung out of her diaper on the side, and we just needed to wait for her to pee. She seemed irritated by the bag, but she was very pleased with the bottomless supply of apple juice in a juice box (a first for both kids).
Miles also did his part to show her how to down that juice box.
After about half an hour, Vivienne filled up her little bag. The initial results didn't show any sign of a UTI. They cultured the urine overnight and called the next morning to inform us that she was all clear. We couldn't figure out why she had started crying so badly that night after that bath. We never saw any other signs of her having a UTI, and it's been smooth sailing for about a week now.