The reading course should teach your daughter many techniques that will improve her reading comprehension. Carefully study all the reports on your daughter's progress in improving her comprehension. If possible, discuss the progress reports with course teachers to have all your questions answered. They should know if your daughter is going to need more help with comprehension next year. These teachers should also be able to recommend tutors that will reinforce what your daughter has learned during the summer.
You're right about your daughter needing good reading comprehension skills in high school. The reading load will increase tremendously, and most students don't have the time to read and reread assignments in order to understand them. You've certainly done the right thing by enrolling your child in a summer course.
You might also help your daughter build her vocabulary during the summer. The larger her vocabulary is, the more successful she will be in school. At her age, most children expand their vocabularies through reading. Do encourage your daughter to read this summer for 30 minutes every day. Also, you should read to her to expose her to even more new words. Be sure to talk with her about what she reads and what you read to her.