It might have been kidney failure or a diabetic coma into death from non-treatment.  She was eating pure refined sugar, either could be possible.  Fat kidneys are typically unable to handle the lifestyle of fats and eventually start to shove sugar through them. This swiss cheesing of their kidneys will eventually cause failure.  The frosting could have spiked her blood sugar so high that her body shutdown to try and filter out the syrup that is her blood, but that could result in a lack of oxygen to the brain and death particularly since she was sitting up.  And if she shifted into a position that had limited breathing ability (like one where her fat is crushing her lungs), this would almost certainly happen. Edit: The kidney failure leading to death would be a lethal level of toxic poisoning, which is hard even for deathfats to get to.  So I'd bet on the coma death.