Honestly,I really don't think there is a cure…but keep hoping and watching the tread for real magic solution.I've got one who feather picks and I've tried everything. the strangest thing is she only eats her own (moulted) feathers or picks from the other girls shoulders, just at the very top of their wings. I suspect it's more of a dominance behaviour as she is well fed and gets loads of mealworms, oatmilk porridge and probiotics so she cant be protein deficient. I've tried all the usual things, No therapy works while I'm with them but not when I'm out of her line of vision/earshot and she seems to actively like the taste of antipek spray and chilli (yes I did rub a tiny bit of chilli on one of my girlies baldy wing bit) It made her peck even more. The OP's suggested product seems to be an american only thing, is there something that we can get in the UK to help get her to quit?
But try spraying the blu note on the favorite ares on those being pecked. They really hate to get that stuff on their beaks.