When I took Finn to the vet recently, my vet agreed that he could spare 8 or 10 pounds. She said that if I didn't notice any weight loss after decreasing his meals and exercising him more...and, I noticed he seemed to be having allergies...that I should bring him for thyroid testing. And, as has already been said, the thyroid problem doesn't go away, but, it's controllable with medications. If Finn doesn't lose weight after a couple months (which he's already lost 2 or 3 pounds!), I'll take him in for testing. But, allergies (like your dog's rash) are one of the signs that something might be wrong. I hope your girl reacts well to the meds!