I would have gone with:
1. Average height of an American female is 5'4". Based on this, she appears to be average height.
2. The length of an average female's hand is 7.1".
3. Coincidentally, the width of the average 36F bra cup underwire is 7.1".
4. The average width of the straps of a knapsack is 2.5".
So... she is wearing black underwear, and her name is Jennifer.
Unrelated facts to conclusions rocks! Yay ignorance!