Disarm her

You don't need your military knowledge to decide your first step. It's obvious that Joanne is only dangerous because she is allowed to carry a weapon. If you manage to force her to hand-to-hand combat she is powerless against your fighting skills. But you must be quick and strong to disarm her. To your luck Joanne doesn't change her tactic until it's too late.

In the moment she aims for your head and swings her iron bar you raise your right arm to block her strike. Your arm takes the full force of the attack and it's a tingling pain but this allows you to grab the bar with the other hand and hold it. Joanne tries to get back control over her weapon. She pulls, shouts and even kicks at you. But even with one hand you are strong enough to hold the iron bar. Then you use both hands and pull strong on the bar. Joanne stumbles forward, looses her hold on the bar and bumps into your chest.

While you throw the iron bar out of the ring and so out of Joanne's range, she jumps back before you can grab her. She is still ready to fight but without the weapon she is not that dangerous anymore. And when you look in her eyes you can see that she knows it.