None of these tests have limited access based on age. Are you 100% positive that access to college classes where you live would be limited by age? That is really rare and our experience is that there are often exceptions to that rule.
My suggestion as the parent of a college student with special needs would be to do all you can now to focus attention on working on the writing issues. It is a better place to focus energy than working on college credits now. Even with accommodations it is really hard to function in college with significant writing difficulties. The same skills called for on the AP tests are ones that will occur again in college courses. I feel like time spent on OT and really working on this was time really well spent.
She may be happier to have some of those intro courses the first year she's in college so her load isn't so heavy. A lot will depend on the kinds of schools she's thinking about. CLEP will get her nowhere at highly selective schools. A lot of state universities don't care about SAT IIs at all. There is really a ton of information on the College Board site. Just to take an example - University of Michigan - grants CLEP credit for very few courses.
http://collegesearch.collegeboard.com/search/CollegeDetail.jsp?profileId=6&collegeId=1195 They do grant AP credits.
http://www.admissions.umich.edu/admitted/freshmen/adv_credit/ap_guidelines.php
