When our daughter was two we hosted a French exchange student. My wife and I had visions of an unpaid au pair. Was the girl supposed to be a student in high school or an employee? When our children were small, we had several au pair girls from Europe, but they were all paid under the program we used. Nice girls, some had better work ethics than other, some were better educated than others, some got a great deal out of their year in the US, others less. We included them in all familiy activities and vacations on an equal footing, as the concept au pair dictates. In several cases we met their parents or other relatives who visited. Overall, a wonderful experience.
If she was supposed to be a student, I should think your view of her as an upaid au pair was unreasonable and denigrating. If you went to Europe expecting to be a student, taking part in typical student activities and spending your time (when not studying) with other students, I'm sure you'd be surly if treated as an employee and put to work.
French personal hygiene habits vary, I have met Frenchmen and women whose habits are similar to those you describe, but also Frenchmen and women whose hygiene would satisfy the most fastidious.
I meant this post as a light-hearted view of my own experience with the program - I certainly did not expect to be cast as Simon Legree. To clarify, we knew all about the program and what was expected; we bent over backwards to include her in all activities. We HOPED she would help watch our daughter from time-to-time, certainly less that what we would have expected if she had been a member of our own family. Not only would she not help out around the house at all, she did not want to participate in any of the activities we planned for her, nor would she willingly participate in any of the group activities the other exchange students were doing. It was obvious she was here only because her parents made her and she detested America. I suppose we got a lemon; I know others who had charming students, but we do not think it is worth the hassle and risk to do it again. Also, I disagree about your views on European bathing habits. Have you every been in a crowded Paris Metro in mid-Summer? Euros do not bathe as often as Americans, as a rule (I know some do). I lived in Europe for six years so I know what I am talking about.