Final answer:
The 76-year-old female is experiencing left-sided heart failure, as evidenced by her symptoms of pulmonary edema caused by the inefficient pumping of the heart.
Step-by-step explanation:
The 76-year-old female presenting with symptoms of shortness of breath, lower leg swelling, jugular venous distention, and crackles in her lungs likely has heart failure. Given that she also has hypoxemia with an SpO₂ of 90% and crackling lung sounds, this points to fluid 'backing up' in the lungs due to the heart's inability to pump efficiently. Specifically, these symptoms are indicative of left-sided heart failure, which results in a rise in pressure entering the left side of the heart and subsequently causing blood to 'back up' in the pulmonary veins and capillaries, leading to fluid leakage into the lung tissue and creating pulmonary edema.