She is 25 years old and in the prime of her career. She is faster (as evidenced by her 200m time earlier this year) than she was as a kid, plus the 400mh is the one event where you see dramatic time improvements as you get more proficient at the event. She is running new step patterns and eliminating strides, which makes her faster and as she gets more proficient at it, she keeps her speed and velocity over each hurdle versus chopping and slowing down like the people she is beating.