wow @ ladyjane's sunny d! he is gorgeous, what an improvement!
zowi also takes melatonin although i am thankful she does not have any hair loss. she did have a small skin infection, losing a little hair on top of her head and around her eyes, but we took her in right away and it was treated with the antibiotic simplicef. in a week it went away and the hair has now grown back. (no prednisone could be prescribed because she has cushing's.) when she was 1st diagnosed with cushing's we tried the melatonin implant, specifically dermatonin brand. (it was being given for hormonal reasons rather than coat improvement.) after 4 months we switched her to oral melatonin hoping for better results. i was told by her dogtor when we started it that it is pretty safe and she has personally never seen any ill side effects from it in any of her patients, so for reese, it sounds like it could be a good start.
unfortunately, vets truly do not have much knowledge when it comes to diet... most tend to push brands they sell/carry. consulting a nutritionist is a possibility, others here might be able to recommend a great one but personally, i can't. you must find whatever works best for reese. this can be extremely difficult and trust me i have been there. the only advice i have for you on that subject would be to use caution as you switch her diet and do it slowly so her system can adjust.
sending well wishes, hugs, and prayers for you and reese to get all of the answers very soon and get her all better! also providing you with a link to acvim to find a veterinary specialist in your area, if you choose to do so. (dermatologist or small animal internal medicine or even better to find a specialty clinic that has both, which shouldn't be too hard to find!)
ACVIM