I think starting with Python is a good idea, I recommended this to a friend for her daughter for the same reason. Python has the advantage over Java & C that you don't need as much ramp up time to getting a program on the road. I also think this is a VERY good idea for her to start this summer. A beginning programming class can be extremely time intensive, just to set the system up and to crunch through the first programs. I taught myself Python just by going to the Python.org site and reading the docs, but that was after years of experience. On there is the misnamed book "Learn Python the Hard Way"
http://learnpythonthehardway.org/book/ that I like.
If your daughter is motivated enough she shouldn't need a class to get ready for a class. I also liked CodeAcadamy, it's a bit simple. But it's very straight forward and gives the basics to quite a few things.