I totally understand your concerns about your sister's health.
The following points should be taken into consideration.
1- Your sister has multiple heart problems that are all connected to each others (
cardiomyopathy, atrial fibrillation, and
heart failure :
Ejection fraction of 15 to 20% as i understand from the history you presented). The main reason for her
difficulty breathing is her heart problem because blood is entering the heart with difficulty from the increased pressures due to heart failure leading to congestion in the lungs, which is so typical in this case.
2- however always in acute exacerbations of lung problems weither in heart patients or no, a problem within the lungs themselves can be the reason for this difficulty breathing. A
lung infection ( pneumonia ) , a lung disease ( interstitial disease ), COPD exacerbation ( infection leading to exacerbation of respiratory symptoms of patients whith COPD), exacerbation of asthma if the patient has asthma. Or even sometimes an upper
respiratory tract infection such as flu can cause difficulty breathing.
3- The following steps should be taken into consideration : A
complete blood count , a chest X-ray, an evaluation of heart with heart ultrasound should be done in order to detect the problem and optimize treatment based on the detailed medical history and the findings of physical examination
Best regards