It should be fine to skip prealg. You, Val, just need to monitor and detect if your DD9 is not undestanding something as well as you'd like, and work to strengthen that. You can also look at a list of typical prealg topics and quiz her to make sure she's got it all.
I didn't go through the US system, so I'm only now getting familiar with what's in these courses. I find it interesting when people say you can skip prealgebra or precalculus, or they say they didn't have such classes when they were in school. But somehow AoPS finds enough content to write a 608 page prealgebra book and a 528 page precalculus book (and to slip an algebra 3 class in between alg 2 and precalculus). Perhaps AoPS courses are a mile wide and a mile deep, while some school courses are an inch wide and an inch deep.
