If Johnny or Reed were paying attention, they could have heard Sue coming by the distinctive click-clack sound a woman's shoe made when she walked, especially when she walked fast, as Sue was. When she reached the lab, rather than waiting for the doors to open for her, she forced them to open faster using her powers.
"Johnny! Reed!"
She was not happy, and that was very evident from the expression on her face. She, too, had a tablet with her, and wasn't feeling very patient that day:
"One of you had better explain to me why our systems alerted me to suspicious activity on Johnny's e-mail."