My own experience from going to a public elementary school in CA, to a private Christian school (which did the ACE curriculum) with much higher standards in AK, and then back to a public high school in CA was difficult socially. I wasn't accepted in elementary school, when I moved to the ps everyone all ready had friends and didn't want to include me, and then back to the hs with all the same kids from the elementary school was just as cliquish and bad, though there was a bigger pool of people to find one or two friends in.
I doubt if things are going to go much better for your daughter than it did in elementary school.
Are there no homeschooling groups in your area?
Our local hs opens up their sports teams sometimes to kids out of the school. Or maybe your hs has after school groups that she could join, without having to completely switch. I attended an International Folk dance group that was affiliated with the hs, but open to everyone. It was one of the best experiences of my hs years.
Our local CSD also offers classes for hs aged kids.