If schools weren't so concerned with testing, then there wouldn't be a need to play "catch-up." Personally, that's a pretty light load. I was in high school ten years ago, and I had to read 5 books every summer.
Your daughter hopefully isn't being forced into doing that other stuff. Education is
so important throughout life. (I agree with the AP stuff- it's good to take those classes, but there's no need to take those exams.) Complaining that there's too much work just instills in your daughter that if it's too hard, it's not worth doing. Hey, she's learning how to multitask- something she needs to learn in college! (Unless she's getting her Bachelor's in Partying...)
To the other posters that are complaining that school breaks are meant for doing nothing, I feel bad for your kids. They need to enjoy life, but they also need to be shown that there is more to life than video games and binge drinking on the weekends (I'm sure your kids don't do that stuff, but I know plenty of high schoolers who prefer to drink and smoke instead of doing something productive). That being said, if you don't like the school, just homeschool your kids. I'm sure you know more than the educators who are paid to teach it.