We also use k12 and while we don't stick to the curriculum exactly DS6 really enjoys it for the most part. As long as your DD can pass the assessment it doesn't matter HOW you teach the lesson - so feel free to let her go off on any tangents you desire and then take the assessment when done (there's no way she won't be able to pass the assessment if you're going more in depth!)
You can also 'rush' her through the 1st grade science (or any subject) by assessing out of things she isn't interested in doing - that way you get to harder things more quickly.
We're in the process of adding my K'er to doing k12 so our lives will become more messy (umm interesting I mean) in the next few weeks. Neither one will be at level yet but we're getting there.
I do love the fact that we were able to quickly get DS6 into 3rd grade math and he is 1 unit away from finishing the 1st semester of it already. We're almost to new stuff even - so far only a few concepts or words have been new to him but he's happy and enjoying it still so all is good I think.
