My dog poisoned? Or had a heart attack?

My dog has died, I need to know why. She (babydog) was 11 years old in human years, guessing that makes her somewhere around age 55 to 77. She is a chow bred, weighing around 75pounds. Starting three days ago she stopped eating or drinking water and her ear was swollen so I gave her two aspirin and sprayed iodine in her ear. The following day she would eat NOTHING, the third day she began to swell and color began leaving her mouth/gums and then she got to where she could not walk, I called a vet at night the vet said give her two aspirin and a benadryl but I could NOT because her mouth was 'locked' she couldn't open her mouth and I couldn't pry it open. She died in my arms. Only thing I could see was her abdomen was swollen and her jaws had 'locked'. Are these symptoms of poisoned or heart attack? She was the only dog I have ever had that would have probably died trying to defend me, she was/is a VERY special dog to me, I'd like to know why she died. PLEASE HELP and thanks to all that can shed to light on me to answer the question.