Liz Picket is a surgical nurse working at New York General Hospital.
She assists Dr. Madeleine Enright on the surgery of energy CEO Oliver Veldt. Actually, she was secretly working for Alistair Wesley who was blackmailing Dr. Enright to kill Veldt. In case Madeleine failed to murder Veldt on the operating table, Picket, being the back-up plan, was supposed to kill him.
When Madeleine refused to kill Veldt as planned, Picket nicked an artery in the hope that he would bleed to death. However, she was knocked out by Finch, who was posing as a doctor, and Madeleine was able to operate on Veldt and save his life.