Susan knew that even though her brother could handle a sword, there was no way he would be able to beat Ivan, who was more skilled and experienced than him.
When Susan noticed her brother was beginning to struggle with the fight and was only defending, with Ivan not giving him any space to recover and fight back, she also picked up a sword, which she held up with two hands because of how heavy it was.
She wasn't sure what to do until Ivan knocked Williams to the ground and was about to strike him when she used her sword to stop his midair.
Her hands were shaking together with the sword as it was too heavy for her, especially when Ivan continued to push it down.