If there is a problem with food or with the stuff your dog eats on her runs, allergy to a plant or a particular ingredient of the dog food is the most likely problem.
(a problem with food or with the stuff; eats; your dog) (a problem with food or with the stuff; runs; your dog) (allergy to a plant or a particular ingredient of the dog food; is; the most likely problem)
a problem with food or with the stuff a problem with food or with the stuff allergy to a plant or a particular ingredient of the dog food
eats runs is
your dog
your dog
the most likely problem