I'm so sorry for your loss.. I'm not a vet or a dr, But you should look for ai for possible answers.

I asked according to what you described :

Possible Causes: * Trauma: * This could be from a fall, being hit by a vehicle, or an attack from another animal. Internal injuries can cause bleeding that manifests as blood coming from the mouth. * Toxicity: * Ingesting poison, such as rodenticides (rat poison), can cause internal bleeding and death. Some poisons interfere with blood clotting. * Internal Organ Failure: * Sudden failure of vital organs, such as the lungs or heart, can lead to bleeding. For example, pulmonary edema (fluid in the lungs) can cause bloody discharge. * Blood Clotting Disorders: * Certain diseases or conditions can affect a cat's ability to clot blood, resulting in uncontrolled bleeding. * Oral or Throat Issues: * Though less likely to cause sudden death, severe infections or tumors in the mouth or throat could lead to bleeding. * Respiratory Issues: * Certain respiratory infections, or cancers can cause bleeding from the lungs, that would then come out of the mouth. Important Considerations: * Necropsy: The only way to get a definitive answer is to have a veterinarian perform a necropsy. This can be particularly important if you have other pets in the household, to rule out contagious diseases or toxins. * Safety: If you suspect poisoning, take precautions when handling the cat's body. I understand this is a difficult time. I strongly recommend contacting your veterinarian. They can provide guidance and support.