I think it also depends on the type of bike she was riding. A road bike with 23c tires and caliper breaks has a completely different stopping power than a mount

I think it also depends on the type of bike she was riding. A road bike with 23c tires and caliper breaks has a completely different stopping power than a mountain bike with 2.1 tires and disc brakes. In an emergency breaking the former would lock the rear wheel and/or lose the front of the bike (rider would fall to the side), whereas the latter would have much better control with reduced wheel locking. From my own experience, stopping a road bike at ~40mph in around 100ft is an optimistic estimate, specially if you are going downhill.