I would be cautious about community college dual enrollment in place of AP or IB courses for a student who intends to pursue a four-year degree. In my experience, community college courses are a fine substitute for standard high school courses, can help homeschoolers demonstrate that they can succeed in a classroom environment, and are a great way to expand access to college for students who could not otherwise attend, but they do not really substitute for AP/IB or four-year college courses. Some four-year colleges allow high school students to take courses for credit during the summer term or through dual enrollment during the senior year, and I'd encourage this over community college.
Even if a student does not receive full college credit for her AP and IB courses, these courses will help with college admissions. Colleges are looking for students to take the most rigorous high school courses available.
If you are looking to save on two years of college tuition with an AA at high school graduation, will your child graduate college at 19 or 20 and then move on to grad school or a job? I have seen very, very bad things happen when 19-year-olds attend grad school. It's also unlikely that the AA will fulfill the prerequisites for the major, so realistically you're still looking at 3 or 4 years at the 4-year school.