I value veterinarians hugely and respectfully understand the challenges they are working with especially in animal medicine.
I simply consider them to be human and possibly have off days, miss something, or even just have it slip their minds.
I also recognize that vets many have different perspectives than each other and ALSO different training/accreditation and/or resources/equipment, etc and not all are created equal. Some graduated at the bottom of the class as well. NO disrespect intended to them.. I question EVERY thing.. in order to be informed about the choices I make, NOT to be disrespectful, hopefully!
Also, if I do THINK one has completely missed the boat.. am not above completely disagreeing with them.. either it helps or I learn WHY they were correct.. some aren't worth the salt in the sweat on their brow.. straight give bad advice.. even treat their patients poorly and should lose their license to practice all together.. what goes on behind closed doors can be WELL hidden to the public. One local vet told a poultry keeper to put their bird into a feed sack with DE and shake like shake N bake to combat poultry lice/fowl mites. DE is completely ineffective in humid environments like or local climate and that was harmful advice IMHO.. and I let them all know that.. USE something that
works IN YOUR area and also withOUT harming your animals!! Sorry for the mini vent.
ALWAYS question authority, seek the truth.
Since B vitamins are water soluble any excess will be passed in droppings. I know they help support many things immune system related and truly do not believe they will be harmful or would not suggest it, though admit to learning something new DAILY. Consulting your veterinarian who is overseeing your gorgeous bird already would be a good choice.
ETA: you should be able to test for west nile.. I volunteered at a wildlife rehab where one of the Harris hawks brought in by the public had west nile and completely forgot how to eat. We hand fed it hunks of BOP (ground bird of prey, meat.. likely horses, etc.. used in many zoos) shoved down the throat.. the bird literally could not swallow. It was still doing well but my time was up before the end of the story.. Wild animals which cannot be released back but do recover are kept in zoos for "educational" purposes.