I have a 12 year old and here is the list of things she will be doing this summer:
Volleyball Camp at the High School (2 hrs/day for 2 weeks)
Tennis Camp at the HIgh School (2 hrs/day for 2 weeks)
Volunteer at the Library for their summer reading program (2 hrs/week)
Leader-in-Training camp for a park district camp for 4-5 year olds (3 hrs/day for 2 weeks)
Overnight camp (one week)
It sounds like my daughter will be busy, but these activities are all for only a couple of hours each morning. She will still have time to hang out with her friends and go to the pool. I agree with you, you need to have some things scheduled- you don't want to hear how bored she is! Have her ask her friends what they are doing. She might be surprised that everyone else is signed up for stuff! And you need to know now so you can sign her up too!
Make sure you check out your local park district and high school for anything that is of interest. Good luck!