I so know how you feel. When I was in college I worked at a YMCA day camp (usually with 5-6 yr. olds. One day a fellow counselor called in sick so I took her group for the day (a group of 9-10 yr olds.) There was a girl in particular that was very nasty, started alot of fights between kids and was very belligerent towards me. I had finally had enough of her after about four hours and went through disciplinary measures ie..verbal warning, removal from activities, and eventually a discipline report home to parents. The next morning I was met at the day camp door by police, the YMCA director, and the girl's hysterical parents. To my utter horror, this girl went home and told her parents I groped her privates. I had a total heart attack! After several hours of intensive interviews, they (police & YMCA) finally realized there was sufficient reasonable doubt to bring the girl in for a psychological review. Well, of course, midway into it she breaks down and admits she made it up. It so didn't matter at that point. It was a major blow both to the YMCA and to me personally. To this day, I am hyperaware of children and my interactions with them. Fifteen years have passed and I still remember her name and what she looked like. It was easily the most damaging thing I have ever encountered. And the really dumb thing about it was the girl's explanation. At that time I apparantly was considered a "cool" counselor and when this girl first acted out, and I corrected her, she took to heart that I hated her and therefore went on to worse behavior out of embarassment and pride. I know I probably handled her wrong as far as maybe I was too harsh or something in my words. Of course, there were no repercussions for me and I even eventually sat down with her and her parents who suffered severe embarassment and humiliation but had the guts to come to my house and thoroughly apologize.
My advice - reach into your memory of the night and think if you might have embarrassed this little girl and projected some type of dislike. Then ask for a sit down with a mediator and confront it with the girl herself...but I can say from experience...DO NOT LET IT GO! Something like this will fester in your mind and influence your life negatively if you don't resolve it. Even if it is a simple misunderstanding...make sure all parties know this (the girl...not the mom necesarily cause she sounds like a nut!)Good luck!