Does a miscarriage at the ninth week of pregnancy necessitate ghusl (post-natal bleeding ritual bath), and does it have the form of a human being?

You are not a nifas (postpartum bleeding) woman, because the minimum period for fetal formation is 81 days. What you are experiencing before this period is considered istihadah (irregular bleeding) and not nifas. So, your ruling is the ruling of a woman with istihadah, and only the blood that coincides with your regular menstrual cycle from this bleeding is considered menses.