FYI, the AoPS Pre-Algebra book covers a lot of territory, but provides a pretty full explanation of everything you need to get through it. Major prior knowledge may not be essential if your DD is feeling ready to deal with the material.
We did it with only grade 4 math, and while DS didn't know most of the topics coming in, we never needed to look elsewhere to fill in gaps: the book is quite comprehensive. If your DD is doing the work on her own schedule using text/ videos/ Alcumus (not an online course), she could take as long as she needs and so wouldn't have to worry about falling behind on sections that are new topics.
