Just to play devil's advocate here, what makes you think it is the food?
It could be that there is something in that food that she is reacting sensitively to, but not likely given that she did fine on it for as long as she did and the problem was sudden.
It is also common for dry dog foods to have a lot of bacteria - if you get a bad batch/bag, this can be a problem. But it is not likely bacteria since you said you fed pumpkin and this helped. True bacteria would feed on the fiber, and the body would have likely "flushed" harder if you will. So the fact that the pumpkin helped in the intestine, points to another culprit.
I just had this problem in my house actually - horrible diarrhea and foul odor from the gut. Very unusual at my house too. Three dogs here - two girls are mine and raw fed and I have a foster boy here who is Nature's Variety Raw Instincts. My girl got it first, then my foster boy the next day, and then my other girl the day after.....it was clearly contagious whatever it was - and it wasn't food related since they all eat different diets. Pumpkin also helped in my case, and a blood test and fecal test on the girl #1 showed no infection or parasite outside of the digestive tract. So that left potential viral infection in the digestive tract, or the consumption of something somewhat toxic. Consensus settled on the former.
All three dogs went on a bland homecooked diet while they healed - ground turkey and pumpkin or ground turkey and white rice. They got grapefruit seed extract to treat anything viral (or bacterial) as well as licorice root and olive leaf for the same. They also got digestive enzymes, Digestinol for inflammation, and Primal Defense probiotic, plus two Standard Process supplements to cleanse the bowel: Gastrex, and Okra Pepsin. They are still getting the last two even though they are all back on their regular diets, including my foster boy.
My point is just that there may often be a bug - kids and dogs get bugs that can be from something they ate - but they need time to heal and changing foods may not provide the results you are looking for while the digestive tract is inflammed. I have several friends who are reporting similar issues in their dogs as well right now....not sure what is up, but just be aware....