That she missed is irrelevant. She tried to kick him in the groin, a serious attack. Absent some justification that is not present in the video, she committed assault. She lingered in range, able to renew her attack instantly... as she actually did after his first return punch, she hit him again, he hit back again. Based on the vid alone, I see no justification for her actions. Based on the vid alone, Green could have a self-defense claim that stood a good chance in court (in most US jurisdictions).
If someone swings, you don't have to wait for them to connect for it to be self-defense. In fact, you don't have to wait for them to swing, if they're acting like they will.
Sports are entirely different. There are rules in sports. On the street, there are limitations on how violent someone can get. To all appearances she INITIATED the assault on someone twice her size, so that is her fault for starting it.