my 12 year old deceased shepard

Question
Hi,
My 12 year German shepherd passed away monday night,but I'm not sure if it was old age or was she poisoned?

She was behaving like an old dog, slower than normal but still eating and barking.  On Monday evening she did not eat her food, rather she drank her water like mad and was putting her paws in the water bowl, I found the bowl empty which was strange because I had filled it up the night before and she has never drank all of it in the past.  

She could hardly hold herself up, the next morning I found her dead near her kennel and a bit of blood coming through her nose. Do you have any answers for me, I'd to think that she was poisoned.  Please help.

Thank you

Answer
It is hard to say.  The symptoms sound like  rat poison, but could be something else, or she may have caught and eaten a dying or dead rat.  If she was allowed to run loose, she may have even found the rat poison somewhere.  Please don't add to your pain by blaming your self or anybody for what may have been an accident or even old age.