Well the great news is that the SCM History/Bible/Geography guide and the SCM Enrichment guide are both designed for all grade levels. Depending on what your 12th grader still needs as far as credits, what you have may be usable for both students. Just purchase the books for 10-12 in addition to the 7-9 books. You can find a brief summary of what 12th grade “individual plans” would include here https://simplycharlottemason.com/planning/curriculum-guide/individual-graded-subjects/
You may need to add government or economics if that is required in your state. Here in California most 12th graders are done with required math and science and are just doing extra higher level science.
I think we could be more help if you shared what credits your 12th grader still needs.