Pregnancy can cause dilated cardiomyopathy causing systolic dysfunction.

Dilated Cardiomyopathy can happen in pregnancy (FA 2019 305), but sometimes with less time on your hands it's easy to get overwhelmed with answer choices that all seem relevant. You really have to notice, this person has left heart failure (SOB with lying down) --> lungs (crackles) --> to right side heart (pitting edema). So the answer choice you pick has to explain these symptoms.

• Amniotic Fluid Embolism is usually related something causing amniotic fluid to get into mother's blood supply. They wrote uncomplicated vaginal delivery, so unlikely to be amniotic fluid embolism.
• MDD does not fit this vignette - just one week history of fatigue and there are so many other symptoms to worry about first.
• Pneumonia: 3 day history of non productive cough make it a little less likely, esp with fluid overload. That's not typical in what I've seen for pneumonia questions.
• Pulmonary embolism - she is tachycardic and has tachypnea but this usually presents acutely and fluid overload in this patient makes it less likely.
• Pulmonary fibrosis: she has orthopnea which made me think there's gotta be something wrong with the left heart first so probably not this.

"Postpartum cardiomyopathy, also known as peripartum cardiomyopathy, is defined as the new onset of heart failure between the last month of pregnancy and 5 months post-delivery with no determinable cause" - NCBI