The best way to add bulk to a dog's diet is feeding bone. It will harden up the stools and give the dog natural vitamins and minerals.
Personally, I would skip all carbs and grains if she is having problems with diarrhea (sorry not familiar with her exact problems). The dog's digestive system is much shorter than a humans in comparison to their body length and therefore it is common for carbs to not break down fully to absorb while in the small intestine. They then can irritate the large colon causing inflammation, which in turn causes diarrhea. There are no nutritional reasons to be feeding grains/veggies to a dog.
Cat maid to:
Puddles, female Himalayan (16 yrs)
Jasper, male Ragdoll ?? (approx 9 yrs)
Sweet Pea, female silver tabby DSH (approx 7 yrs)
Rose semi feral, a cpietra rescue, female tabby (approx 6 yrs)
Snowball RIP (1991-2005)
In a cat's eye, all things belong to cats.-English Proverb
“While we are free to choose our actions, we are not free to choose the consequences of our actions.” Stephen R. Covey