This patient has blue lips because she has methemoglobinemia. A number of drugs will cause this abnormal state of the hemoglobin molecule including pyridium, dapsone, local anesthetics, and nitrates. In methemoglobinemia the blood will appear a chocolate brown color, and cyanosis will not improve with oxygen.
Treatment is with methylene blue administration.
Methemoglobinemia is induced for treatment of a cyanide overdose.