20 points is a large jumpb but I think your plan is still good. It sounds like your DD will get to test out of 6th grade math and basically do pre-algebra in the fall. For what it's worth, my DS started pre-algebra with a similar MAP score.
By the way, I don't think a 264 MAP score means that she has mastered Algebra I. It's still a multiple choice computer test that covers a lot of ground. For example, I think DS was able to guess some of the basic trigonometric questions even before he covered Sine, Cosine, Tangent, etc. in the basic trigonometry chapter in his pre-algebra book. (Actually, pre-algebra is a misnomer and that name is being changed in our district since "pre-algebra" actually covers introduction to Algebra, Geometry as well as a bit of trigonometry)
