I second using the Iowa Acceleration scale. You will be able to look at a lot of objective factors when making your decision.
I wouldn't say that not rocking the boat is necessarily a sign of not needing a skip. My DS would happily coast through school with no challenge if he could. He is a teacher pleaser and doesn't like to stand out, so he would never make waves at school. He would complain at home about being bored before the grade skip. [Incidentally, he still complains about school, and now wishes that he wasn't in an accelerated program, because he misses being able to just read his own book and not pay attention in class. Since he is one of the top student's in his accelerated program, there's no chance he's going back, because we want him to be challenged now, rather than be shocked when challenged for the first time in college.] I'm not saying this is what is happening with your DD, but it's something to consider.
