Sorry, I crossed posts with CFK and polar bear.
I wasn't directly involved in the conversation between DD and her teacher re the choice to do Algebra II. The teacher told DD that her class will take her about half way through what they cover in Algebra II at the high school. Now that the teacher knows DD and has seen how she thinks about math, the teacher thinks that the repetitive material and pace will not fit DD. I think that this is where the idea came from. The teacher gave DD a couple options for completing the material. One was through an online class offered by the district that would have to be completed by the end of the school year. The other option was to do a hybrid of Khan/Aleks and do a self-study that she could finish over the summer. DD liked this option better because she has a lot of homework and extra curricular activities right now. The teacher did not seem to think that the Algebra II material would be dependent on anything that she would learn in Geometry.

As for how far the high school math goes, I think that they go through BC calculus and have AP statistics. There are off-campus options at the local university or community college but they will take some juggling.