A couple of suggestions...
First, do stick to the fifteen minute rule. One thing that has worked very well for me is to take a great quality kibble, soak it in hot water for fen minutes, then puree it with cooked chicken or hamburger (including the juices). Start with mostly meat, then, if she begins to eat better, slowly increase the percentage of kibble. If you try this, you can make up several meals worth, freeze them in baggies, and warm them in the microwave just before feeding. Almost all dogs prefer warm food. The warmth and moisture make it prone to spoiling, though, so be sure to pick it up and dispose of it in 15 minutes.
Another option is Nutri-Cal. It is a dietary suppliment originally developed for dogs with no appetite after surgery. It is a high-calorie, nutritionally balanced, appetite stimulator as well. If you totally take her off solid food for a few days, feeding her only Nutri-Cal (2 tsp per 10 lbs body weight is enough to keep her healthy), it will allow her stomach to empty enough that she feels like eating while increasing her appetite. Along with increased exercise, this regimen should get her interested in food again.
I had a friend with a dog who had a poor appetite. The vet could find no reason for it, we tried every food we could come up with... to no avail. The Nutri-Cal regimen was tried, as well. Finally, the vet suggested giving her aloe vera capsules, in case she had heartburn. It worked! She would get a tablet about 30 minutes before each meal, was offered food 5 minutes at a time 4 times daily, and started eating better. She still gets one capsule daily (after 9 months), but is down to two meals daily.
Good luck!
Beth