had something similar happen to my old dog Chloe. We had just had her undergo surgery to remove a large fatty growth. She started throwing up stuff, and then she had trouble standing and her poop was black and smelled like something was decaying. We finally took her to the vet and found out that her intestine had ruptured(most likely due to an undetected cancer) and she was turning septic. So we had a choice. either operate on her immediately which would cost several thousand dollars, force an 11 year dog to endure a very lengthy surgery, and which would only have a coin flips chance of succeeding, or put her to sleep. We very reluctantly chose the latter, as even had the surgery been successful, her quality of life would be diminished, and there was no guarantee that she would not die during the surgery. I'm sorry for your loss Nahla. Losing a pet is always hard, particularly one that has been a family member for a long time.
