[Acroyali]

I am a raw feeder, so I can’t suggest much in the way of kibble but I have noticed that there have been some tummy-related complaints with Blue Buffalo. This isn’t to say it’s a horrible food, it’s just that some dogs seem unable to utilize it as they should.
I know that Wellness has a very limited ingredient line (4-5 ingredients only) that can be of a big help when it comes to food intolerances. (I believe most of the line includes novel protein sources like duck, etc.)
http://www.wellnesspetfood.com/categories.aspx?pet=dog&cat=3#Simple Dry Limited Ingredient Diets Dog Recipes
I don’t believe it’s formulated for seniors, but it’s just my (personal) opinion that senior diets are kind of gimmicky unless there’s a serious medical reason that specifies a low(er) protein diet.
Fromm is an excellent company that, if I fed kibble, I would feel 100% comfortable feeding. They have a beef formula, no chicken.
https://frommfamily.com/products/four-star/dog/dry/#beef-frittata-veg

Also, it might be worth checking into giving this dog some probiotics and/or digestive enzymes to help digestion. The metronydozale is a helpful drug in this instance and can stop the problem in it’s tracks, but re-feeding her gut with beneficial bacteria might help even out the occurrences of diarrhea. Both probiotics and D.E’s can be VERY helpful when transitioning a dog with a sensitive gut over to a new food, too, so that might be something to consider.

I don’t know if you’ve ever given her pumpkin, but many people swear by it to help with chronic diarrhea and firming the stools.
Hope this is helpful.