If her heart stopped for 20 minutes, that means oxygen isn't reaching the brain. When oxygen isn't reaching the brain, cells in the brain die from not receiving oxygen. So in that 20 minutes, she could be brain dead unfortunately, or have suffered MAJOR brain damage. The only instance in which the brain can go without an hour of oxygen is when you are submerged in freezing waters. I am sorry this has happened but you must face the fact that she could never wake up.