Well, her babysitter is apparently *not* miserable at college, so why assume she's naturally stressed-out?
Honestly, the workload at GDS is pretty intense and there are lots of pretty demanding extracurriculars.
The three-meetings-per-week class schedule seems to mean more classes (and more homework and less in-class practice -- which matters in things like math and foreign languages) than I had in high school.
"Balance" often takes the form of spending as much time doing extracurriculars (sports, debate, drama) as academics -- which can really cut into sleep (not to mention leisure).
The open til 10pm and on Saturdays campus and lots of homework over the weekend can create a feeling that you're never "done" with school (for the day or week). I certainly didn't grow up like that (though I've BTDT as an adult and, yes, it's stressful). For some kids, GDS probably feels like a bootcamp for future workaholics.