Just as well Susan left to go and find quill and parchment. She could have been contrary and just summoned it, but if she stayed in the room any longer with Percy, then he'd have other more life threatening injuries to worry about.
Coming back, she checked to see that Cass was still lying there and not doing anything stupid, overhearing the comment about Percy being a stubborn fool. She snorted in amusement at the comment.
She handed the quill and parchment to Percy. "Here," she shoved it at him, wondering if he was actually capable of writing. "Anything else I can get either of you?" Behind the snarky sarcasm in her words, she was genuinely offering to help.