At this point, this is NOT a simple food issue! Playing around with foods may give short-term relief, but will not remove the problem. The best it can do is prolong her pain.
The question about meds is a good one. Did you give your dog any meds recently? Did you change her heartworm or flea meds? Some dogs are allergic (but then you should see the allergy signs.)
Call a vet. Request just an x-ray, first. Who knows what she may have eaten - a small toy, a bottle cap ... a sock. If an x-ray shows nothing, then consider an MRI.
One step at a time, but at this point, they need to be bigger steps than just playing with food.
No it's most likely not a food issue, but foods and the ingredients in foods can aggravate and feed whatever might be wrong. It's always best to fix a dog from the inside out. Strong gut and immune system and diet will aid in recovery. A blockage is a good possibility too.
I am interested in knowing about heartworm and flea medications. Some out there have killed dogs, it seems to be hit or miss, but Bravecto and Trifexis come to mind as possible issues. I would look at the liver, kidneys and pancreas.
I just hope it can be figured out and soon.