The thing about PS is that only a part of the physical training is PT, by which I mean traditional cals and company runs. Not too far back in the day, PEP obviously included and still includes cals, but about half of it was non-calisthenic PT - for example, fireman's carry relays, or tug-of-war, or wheelbarrow races. There was a strong focus on upper-body strength, and I was kind of surprised to find out that it was not just women who they were concerned about deficiencies.
The other significant physical part of the training is the dynamic, multi-muscle training requiring coordination, or fluid movement. Examples are the O-course, Zodiacs, confidence course, rappelling, water confidence activities, and so on: taking a running jump at a wooden wall and pulling, pushing, swinging, and leveraging yourself up and over; or using your core to balance on one knee while paddling an oar. These are activities that the priors and NAPSters have had experience with, but your average new high-school graduate has not, even though most played at least one sport very well. While cals and running are essential preparation before PS, nothing can prepare you for the dynamic, multiple-muscle-group movements except exactly that. Although it is my speculation, when I think about what I know about exercise physiology now and what I and my classmates were asked to do as plebes, I think this helps explain why some plebes breeze and some struggle (physically). The wrestlers and the gymnasts among us were some of the best at Zodiacs, O-course, confidence course etc. because they had spent years training their bodies to move with precision and to take advantage of the combination of strength and momentum. I will never forget the shortest, smallest woman in my company - probably eked in at minimum height and weight - who could do 11 pullups and one one-handed pullup. (Because of her height, she also took an inadvertent elbow to the cheek one day, splitting it wide open - she went and got stitches, then came back to train with us on what had to be the hottest day ever - she was badass!) There's no way she could catch the top of the wall on a jump, but even she could use her body weight and momentum to help get a 170-pound classmate up and over the wall.
Tothetop14, I would surmise that this was part of the reason your DD felt so well-prepared. Boot camp fitness courses tend to emphasize dynamic stretching and powerful movement as much as classic aerobic and strength training.