I'm sorry I don't have any experience with Thinkwell. However, having some algebra experience before AoPS will be quite helpful. That way your dd can really concentrate on the problem solving instead of also having to get the basic concepts. However, AoPS is quite doable after Singapore. My dd went directly into it from Singpore 6B. At that time the Intro to Algebra class was one course that ran 24 weeks. It is now split into Algebra 1 and Algebra 2, with each running 16 weeks. So, I think the pace would be less stressful now!
