It probably would have annoyed her if she knew his mind drifted even slightly to any other person when she was in there. Did she really expect that he was some sort of good guy? Hardly. Good guys hardly did the sort of things he'd already done with her. Thinking back on the cool wall and his hands on her certainly helped spurn her interest at the task at hand.
She only slipped away for a moment to pay attention to his balls but when she felt the muscles tense she went back to her original task. She didn't really care if they made a mess but he might. She was determined to make him come. She could tell he was at least marginally holding back. She would have told him to not if she could. Instead she just focused harder.