First off, I agree that the second picture is absolutely priceless. (keep in mind for next photo contest )

second, I would have mentioned the diarrhea without hesitation. After all, if they asked about their little girl, then that means they WANT to know.

When Marvin was here (waiting to move to his new home), and kept getting diarrhea, I ALWAYS told his new mom! And I continually added that I would totally understand if she did not wish to take him since we could not figure out what was wrong. And I WANTED him to get adopted, but not if it meant he would be returned due to a problem I already knew about.