Have you tried contacting your daughter's school or school district to see if they are offering summer school this year? If you don't have the school or district's phone number handy (and if located in the U.S.), you may use SchoolFinder to research their contact info: http://www.education.com/schoolfinder
You might also reach out to your city's Recreation Department to see if they are offering any summer learning opportunities. Our town has many options in this regard, and it's worth exploring to see if yours does as well.
There are also academic-focused summer camps hosted by private organizations and nonprofits. You can do a Google search for camps in your area, or talk to other local parents about their favorites. I'm also including some information below about summer camps (as well as about middle school and high school -- to help you prepare for back to school).
Lastly, I want to let you know about another way to help your daughter have fun learning over the summer: Education.com's Summer Activities Challenge. The grand prize is a family vacation to Mexico! There are also great weekly prizes too. http://www.education.com/summer-activities-challenge/