Welp - my husband just brought home a bottle of hydrogen peroxide. I have a large stash of chamomile tea and coconut oil.
What I'll probably do is soak the hair in the chamomile/oil treatment, and then pick a few streaks to test the peroxide on. I'm going to try to keep it off all my natural hair growth, and just go where the henna line starts. Assuming I work up the nerve. A few small streak samples shouldn't be too dangerous though.