Hitting the foot is not done when the opponent forgets to withdraw his foot. Otherwise there would be no hits on the foot on a higher fencing level. In most cases, you make a feint attack towards the opponents arm or shoulder and when he attempts to parry, you hit the foot.
I'd recommend aiming at a higher target, the foot is not practical. It leaves the hand, arm, and face open to a counter attack. The shoulder and elbow are the best targets to attack. The hand is also a prime target, but only if it's exposed.
Thanks for the video. I'm a beginning foil fencer and I'm curious about epee fencing.
I've found her openings many times, and I don't even fence!