Final answer:
The best course of action for the elderly woman with COPD is to ventilate her with a bag-valve-mask device and administer high-flow oxygen.
Step-by-step explanation:
The best course of action for the elderly woman with COPD who is semiconscious with labored breathing and presenting with cyanosis, rapid and weak pulse, and oxygen saturation of 75% is to ventilate her with a bag-valve-mask device and administer high-flow oxygen (option D). This method will assist in providing oxygen to her lungs and improving her respiratory status. Oxygen therapy is crucial in this situation to increase the oxygen level in her blood and alleviate her symptoms.