Immediately stop feeding everything you just listed.
Fast her by skipping one meal as you run out and get a bag of Zignature Zssentials, dry grain free kibble for all ages, #1 for pups with various allergies (which you can do a test panel for).
Take a poop sample and test it for Clostridium (a separate test from the regular Giardia fecal test). Have the vet give her a short IV fluid treatment for severe dehydration.
After test results/or possible antibiotics treatment, get Proviabal (2-day paste, 10 day probiotic pill sprinkle over food).
I went thru the same thing and I had to figure all this out myself, took years. I’d also look to finding a new vet.
