Do we have a case against a doctor that cleared my other on elective surgery?

My mother passed at the age of 74 after being cleared of gastric bypass surgery. I attended all pre-op appointments with her. She clearly was the oldest patient in the worst physical condition. When questioning this, the doctor still cleared her for this elective surgery then insisted it wasn't the surgery that caused her death. She died 3 days after surgery, never leaving the hospital. On day two, she became increasedly weak, aspirated in her lungs, had a massive heart attack. They were able to revive her only to have her organs shut down and pass away hours later.