If the dog has been through several courses of antibiotics, a dollop of yogurt with active cultures in it, may help. Sometimes the antibiotics kill the "good" bacteria in the GI tract, along with the "bad" bacteria.
I'd do the boiled chicken and rice for a while until you get a good firm stool out of her for several days. A dollop of pure pumpkin will help form the stools, too. After she is formed up for several days. start adding her kibble back in, very slowly to see how she tolerates it.
If she won't take the yogurt, you can try acidophilus tablets - I've gotten some in tablet form already that are flavored with strawberry. My fur kids gobble them down like treats.
We had problems a number of years ago with diarrhea in multiple dogs. They kept passing it around. We ran a number of stool samples, etc and couldn't get a handle on it. Finally, they found coccidia. One of our dogs was out showing and he dragged it home. From what I was told at the time, the organism has to be in a certain stage in order to show on the slide when they do a fecal sample- which is what amade it so difficult to diagnose. Once they figured that out, a course of albon finished it off for good.
Another possibility, since she is an older gal, could this be age related? I had an older cocker who started having diarrhea issues. Got to the point I ended up home cooking for him for a little over the last two years of his life. He just coudln't tolerate commercial dog food any more.
I hope you get her straightened out. If you are some place where it's hot, watch her for signs of dehydration. You can offer some pedialyte, as it has the electolytes in it.