With her age, the thyroid condition, being badly bothered by bug bites as well as the "itchies" I would seriously look into an Omega 3 supplement.
Does she have fleas? It sounds like she might have had an allergic reaction to the bug bites & dogs can also be allergic to flea bites.
Several years ago I had a Dal x Lab with Flea Allergy Dermatitis and Seborreah the only thing that calmed the "itchies" was the Omega 3. He was only bathed maybe 2-3 times per year but only in summer outside.