@toromama I googled, "Vaginal bleeding after cortisone shot" and there are a lot of journal articles on the topic. There are also many articles that focus on post-menopausal women and spotting after a cortisone shot. I didn't link any of the journal articles, as they are a heavy read for most people.
It's a concerning symptom no doubt. You are certainly not the only woman that this has happened to. Off the top of my head I'm not aware of a previous discussion on this topic or members reporting something similar.
May I ask if you inquired with your provider regarding this symptom?