He is rolling around on the ground with his hands in the air. She can see both of them. He is not going to reach for another weapon without her seeing the movement. While he is still moving on his stomach his hands are visible. Either way I would have kept distance between me and the perp.
He stopped moving when she got him pinned down with her foot. She probably didn't want to have to shoot him again. If she had moved away and he had reached again she might have felt she had no other choice but to shoot.