First, wow first time I saw your post from 2 mos ago. The old forum really had notification issues so please don't think people didn't care... they probably missed it. Hopefully the new format is helping.
As for >>She was also recently diagnosed with Generalized Demodectic Mange which we now realize had started prior to us getting her<<
Sadly, I have way too much experience with mange thanks to fostering/rescue. ALL dogs who nurse have mites. So yes, your dog had the mites. But if there was mange, you'd have seen signs pretty fast. An actual occurrence can show up prior to a year... which is when it HAS mange. Again, until an actual outbreak, all dogs have the mites. So if she arrived without patches, then the breeder had no way of knowing it would happen. (unless irresponsible breeder who knows their dogs have an issue) Some dogs who in adulthood have severe stress/autoimmune issues/sick can also develop it.
QUOTE: >> It is not uncommon for nursing puppies to become infected with this eight-legged skin parasite during the first two to three days of life. The mites can be passed from the mother to the nursing puppies because the puppies have weak and underdeveloped immune systems that allow the mites to overgrow, causing occasional localized patches of hair loss, redness and scaling.<<
Generalized Demodectic Mange is a sign of immune issues. If this puppy came from a responsible breeder, they need to know. If no signs before, it may really be stress related outbreak and not really generalized (which as this article explains, is defined by, though I'm sure your vet knows. Either way, the breeder needs to know because there are genetic components. Here is a great article.