Welcome to the community!
I'm glad you're getting her tested for PBFD, and make sure that they also run all of the "routine' blood-work as well and not just the individual tests for Avian Viral Diseases, because another huge cause of feather issues in captive/pet birds is malnutrition and/or some type of nutritional deficiency. We all tend to go right to the Avian Viral Diseases, and with good cause, but when it comes to captive/pet parrots, especially ones that you adopt as adults that have already been owned by someone else, you really have no idea what they were fed or what kind of environment they were kept in prior to you adopting them. And nutritional deficiencies develop over-time gradually...And of course with Budgies they are typically fed nothing but a cheap seed-mix that are usually very high in fat, low in protein, low in vitamins/minerals/amino-acids etc., and this can very quickly cause Liver and Kidney issues, as well as issues with their GI Tracts absorbing nutrition from the food that they do eat. And there are many, many health conditions and diseases that can cause a bird to not absorb nutrition from the food that they eat, and they include everything from Avian Viral Diseases like PDD to malabsorption conditions of the GI Tract.
In-general your Budgie does look extremely healthy in that photo...Her feathers are very bright and clean, they aren't chewed-up, at least not badly, her beak and toenails look very healthy, the color of her beak and skin on her feet looks nice a pink and does not show any signs of Anemia, and her weight looks good, she's definitely not underweight or emaciated, so that generally indicates that she is absorbing nutrition from her food. But being undernourished and being malnourished are two totally different things...The good news is that most of the very nasty Avian Viral Diseases also cause weight loss, either due to a loss in appetite/anorexia or malabsorption issues. And she doesn't show any signs of anything like that...
I'd have to agree with your friend who is the breeder that her feathers growing-in oddly/abnormally and falling out easily is most-likely the result of something like French-Molt or some other disease/issue with the feather-follicles themselves, which are extremely common in captive Budgies and Cockatiels as well. And while it's never good to have any type of health issues, this being a localized, non-systemic condition that is specifically effecting her feather-follicles is one of the best-case-scenarios when it comes ot a bird having feather issues...
Keep us posted on how she's doing and what the Vet says. Hopefully this Exotics Vet has a good amount of experience in diagnosing feather/skin issues in birds, and they know what specific blood-tests to run...
***Something that you should mention to your Vet and ask them to also do is to take a culture/swab of your bird's skin, make a smear/wet-mount of the swab, and look at it under their microscope right there in the office, as this can be and often is caused by a topical Fungal/Yeast infection of the bird's skin, and if it is then lots and lots of Yeast will be easily seen on a slide of a skin-swab. That would be best-case scenario, and would be easily cleared-up with an oral or injectable Anti-Fungal medication like Nystatin. This is very, very common in pet parrots, and I've seen topical Fungal Infections cause everything from feathers falling out, feathers growing in incorrectly, feathers not growing back-in at all, to actually causing long-term plucking and self-mutilation issues...This happens because the topical Fungal Infections are extremely itchy so the bird starts over-preening itself, which turns into the bird plucking feathers out to relieve the itching. And what happens is that when a bird plucks a feather out it immediately releases endorphins in their brain, and it feels good and creates what we would call "a high', sort of like a 'runner's high" or a rush that feels very euphoric, just like opiates or other drugs cause. And as a result, even after the Fungal Infection is diagnosed and treated with the proper medications and is totally gone, the bird continues to pull their feathers out because they literally become addicted to the euphoric "high" that they get from the endorphins that are released every time they pull out a feather. So after the Fungal Infection is fully treated and gone, then they have to address the addiction to pulling feathers out, usually with an anti-anxiety drug such as Haldol or Valium, or with some type of anti-depressant drug...You Budgie obviously isn't plucking herself badly, but you did mention that she may be over-preening or plucking a bit, and that could very well be an indication that the issue is an external, topical Fungal Infection...So be sure to request that this vet take a culture/swab from her skin and look at it right then and there in the office, it shouldn't need to be sent-out to a lab just to diagnose a topical Yeast Infection; I've looked at skin swabs under a regular compound-light microscope like they have in Vet offices, and you can immediately see tons and tons of Yeast all over the slide if that is the issue.
