You could be describing my husband and I in this question, his dear sister passed away 8 days ago. We choose to keep the exact manner of death quiet because quite frankly it was painful and we choose to remember her for the person she was in God's name.
Please allow the family to decide when and if the manner of death is revealed.Searching for answers when your not even sure of what the issue is can start rumors and cause undue stress on a family already grief stricken. Allow them their privacy.
I know this response sounds harsh but remember grief stircken families need your support NOT your questions.
Respectfully - if the family prefers to not publicize the illness - as a friend to the family regardless of your goals of becoming a doctor - I would hope you would put your investigation aside and honor the families wishes.
Someone medically must already know what this person past away from and the family chooses to hold that private.
If the recently deceased individual had some sort of connection with you and your thoughts are you may need to know the reason how they passed - If I were you - I would consider meeting with the family and explaining your desire to know the cause of death - Otherwise let the family have their wishes honored.
Have you considered it may have been end stage liver disease? If it was caused by hepatitis c, it has an awful stigma attached to it. I can personally attest that, not only drug users with dirty needles get it...In end stage, the liver fails rapidly secondary to cirrhosis or cancer, the abdomen swells (and feet), and the patient dies...also, severe congestive heart failure can do this too, but the swelling is more widespread...