Erin seemed to play little attention to Stiles because he wasn't an unfamiliar wolf. If Scott hadn't come around, it would probably be a different story. Her focus went to him as he took off and she followed after him with great speed. She probably would have lunged and attacked him is Derek hadn't slammed into it. Being as strong as she was, it didn't affect her much but it made her turn her focus to him instead. She roared at him for getting in the way of her change then she tackled him to the ground. Just as she was about to tear into him, she was tackled by Cora and moved off of Derek. She didn't waste any time in fighting back, of course. It was girl wolf against girl wolf.