Read the whole scenario. She was playing there. Apparently we lose one hair every fifteen minutes. Assuming she was there for only a short period of time she would only shed one hair. This one hair had to make it to the floor and not the carpet. It further had to be washed up by Westerfield and put in the drain and it had to avoid getting trapped (not all hair gets trapped). The sum total of all of these probabilitiers is almost 0. Adding more time spent increased the number of hairs normally falling but it would still multiply out to nonexistant.
Add to the hair, the other improbable occurances and its a very remote possibility the evidence came from a short visit while she played.
Do you really think a hair falls out, on cue, every fifteen minutes? I have no reason to doubt this drop rate, but don't you think it likely that this is an "on average" figure? This would indicate to me, that multiple hairs could have been dropped, or, on the other hand, possibly none were dropped during the time she would have been in the MH. It's all an unknown factor. In fact, we have no way of knowing at what rate of Danielle's hair loss compared to the median, or average drop rate of hair.