That was said, but it was off the cuff "advice" based on nothing at all. Once again, very poor attention to medical accuracy - another area in which Corrie has gone badly downhill.
How many times do you see on here advice about not starting exclusion diets without either/both careful observation or actual allergen testing?
She's how old? One episode of projectile vomiting? This is not how allergies first present themselves, and is typically indicative of some sort of blockage/torsion in the GI tract.
If they want to stay medically credible, then this will need to be a mis-diagnosis storyline.