I know exactly what you are going through because I went through the same thing with my dog. The first thing I did was completely eliminate grains from my dogs diet, opting for a grain free, high quality dog food with venison which is particularly easy for dogs to digest. If the diarreha is really bad, you could use Imodium (crushed and added to food), Pepto Bismal or Kaopectate to your dog's diet or given by mouth.
You could also add rice, potatoes or sweet potatoes to Ellie's diet too, all of which are great for ending the trots.
Please don't let Ellie get too far down because my Pooki ended up having damage to the thyroid and as a result, she has literally wasted away to bones! My Pooki is 15 years old and I realize she is at the end of a long and great life but you never want your dog to suffer and believe me, if they have diarehha, they are indeed suffering.
The food I have Pooki on is Nutro Grain Free Venison with sweet potato.
The worse thing you can do is change back and forth from one brand to another often because it takes a while for the dog to adjust to any food. You might want to just boil chicken and rice with potatoes for a while while her system settles down.