DS10 worked through the AoPS pre-algebra with me this fall, using book (well OK, *I* used the book) and Alcumus (what he did). He had completed grade 4 math, no trace of enrichment of any kind (grr), so was rather light on prep going in. The course was not over his head, but with his focus on just doing the Alcumus problems, pretty much every question required learning a new concept or two he'd never seen before. My guess is your DD would be fine - the book really starts from scratch and assumes virtually no prior knowledge, so it's quite self-contained, but not slow. Everything is derived from first principles (now I actually know why reciprocals exist); I was very impressed with the book and AoPS in general. And the videos were fun (though DS stopped watching after chapter 1 - he was in a hurry).
As just noted on another thread, AoPS without the classes (book + Alcumus + videos) can work very well, if credit is not required. But may be labour intensive on your part depending on how much of a self-starter you have.
P.S. We're signed up for the actual online Algebra starting next week, so we'll find out how heavy the workload can get for a younger kid with limited background.... As quoted above, AoPS says 5 - 7 hours a week including class time, but it would be easy to spend longer if you're dealing with a lot of new material as well as the more complex problems.
