Are you using digestive enzymes on her? You can find this at your local health food store, and they help many dogs process their food better.
Another traditional herb used to soothe the digestive tract is Slippery Elm powder. This is a very mild herb, impossible to overdose it really, you can use it for flour in baking, etc. It has a nice nutty sort of scent, and dogs usually like it.
If the old gal likes eggs, those are a good source of fat and protein for most dogs. Soft scrambled or sunny side up. Other mild things you could give her IF she can tolerate it, include canned fish (salmon, mackerel), lightly browned ground turkey or beef (make sure any ground meat is fresh. Make a big patty out of it, and sear both sides so that it's warm through the middle, but don't cook it well done, leave the inside red....)
Best of luck with her, a 12 YO dane is something to brag about.