I am sorry to hear that you are facing these obstacles. I would affirm your inquiries into dual enrollment opportunities. You should not have to pay full tuition at most CCs in your state (if you are in the same state you appear to have been on your last posting), as your DC is in grade 6-12. Districts are not allowed to deny admission to DE for otherwise qualified students unless they prove (upon admission) to be "disruptive to the learning process such that the progress of other students or the efficient
administration of the hours is hindered”.
Your state does also allow credit by examination, so that's another avenue you might look at, even beyond demonstrating readiness for advanced coursework (as indigo helpfully notes), especially for the autodidact your DC appears to be.
And my sympathies on the frustration. One of ours ended up having to repeat two years of math in high school due to different, but still bureaucratic, complexities (I guess DC did see one new topic--logs, which somehow was not part of the alg II curriculum previously used).
