Sadly I know a lot about this. I am a cardiac critical care nurse. Your friend could have a peri-partum cardiomyopathy. A cardiomyopathy is when the heart is enlarges and does not squeeze the right way. At my hospital, we have seen maybe 5 women in the last 3 years where the enlarged heart is due to the pregnancy. But before this is determined, other things need to be evaluated. Such as coronary artery disease. We look at the arteries supplying the heart by putting a catheter in the femoral artery and injecting a contrast dye. It is visible by x-ray. It is usually pretty harmless. It is iodine based. The docs look for blockages that could have damaged the heart tissue by depriving it of oxygen rich blood. That causes the heart muscle to re-shape. Thus making the heart beat less effectively. Causing heart failure. Was your friend short of breath or having chest pain? I am sure that she has also had a cardiac ultrasound to look at the shape of her heart and the condition of the valves.
Sometimes women with this deliver their babies and are fine. It could just be the stress of the pregnancy. But other times it is more serious.
She should be wathed very closely by her OB and a cardiologist with special knowledge of pregnancy and heart failure. I hope this is helpful and too scary for you. Please support your friend any ways you can. Good Luck to her.