brake failure is a very rare thing but it happens. maybe she was already too close to the car ahead when she realize she had to floor the brake all the way down and ofcourse abs do kick in but u are going to slide eventually because is wet and they work better when u are braking at high speed in wet roads.

35-40mph is slow enough to fully stop and avoid any collision in really wet road as long there is no ice, ofcourse as long u have been keeping a safe distance and u are actually looking ahead and in front.