My findings based on some well known averages.
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".
Without going into too much further detail, but based upon my extensive field research, I have extrapolated that she is wearing (or should be) a 36E bra.
(see attachment)