Isabelle was businesslike.
You could see it in the way she never cried, even when it tore her apart
You could see it in the way she dispatched demons, quickly and methodically
It was in the way she held herself, the way she dared you to criticize her. How she may have been a girl and a flirt, but she never let it affect her job.
You could see it in the way she gained and dumped boyfriends (because who in their right mind would dump her? She was Isabelle Lightwood)
You could tell by her not quite holier-than-thou smile. (Really it wasn't that pious. Just condescending)
Or perhaps by her onyx hair, that could be pulled up into a strict ponytail at a moment's notice.
Isabelle Lightwood was businesslike, so it came as no surprise when she took Simon outside and informed him of their date. Friday night, 7:00, semi-formal.
However, there was nothing businesslike about the way she smiled when he said okay.