raven

I had a female doberman turning 11 this November, but she still acted young and energetic,very healthy,always up to date vet care but suddenly got sick and died on June 2nd. I can't help but wonder what could have made her sick so fast and nothing i look up has her exact symptoms,two different veterinarians,one being her vet she has always seen and the other a local vet in the area we now live since November,have given different answers. we were outside til pretty late on a Saturday night,Sunday she had blackish kind of wet and sticky diarrhea which I thought was due to a different dog food, later it only became worse and one explosive along with some vomiting. she still drank water but I didn't offer her food because of her upset tummy. On Monday I called her veterinarian and was told if she is keeping hydrated she should be ok but scheduled an appointment for the next morning. she did seem to start feeling better around 1:00 pm with her ears perk and wagging her tail but suddenly the vomiting came back which was grass and kinda slimy looking around 6:00 pm. I thought perhaps a warm bath would help her because her paws felt cold but she only seemed weak afterwards, by 9:00 pm she wouldn't drink water or even attempt any food.By 10:00 pm she couldn't stand without wobbling and eventually falling.around 1:00 am she squirted bright red bloody diarrhea and at 4:12 am she died. I stayed up with her all night comforting her and waiting for morning to rush her to the vet since there is no emergency animal hospital where I live but unfortunately I was to late.I didn't have a necropsy done and wish that I had because I can't help but want to know what could've happened. Can someone please help? I don't think it was parvo as suggested because she had the immunization for that. She was last seen by her veterinarian last October just before we moved to another city in South Carolina. The new food I bought was on May the 25th and she only had one bowl on Friday, I checked for any recalls on gravy train but none have shown up. Her usual diet was rice and boiled chicken or some other boiled meat and sometimes mixed with dog food, usually dog chow.