In that older thread, you said that the vet said that it is lupus. You did not say how that was diagnosed? Was a biopsy or culture ever run?
I do not understand why when vets prescribe both antibiotics and pred, and the treatment works, they then say it's autoimmune or from the pred. It could very well be infectious, and with infection is often inflammation.
I wonder, when training, if there wasn't perhaps some exposure to something to something, so this may be unrelated to your other dog. Might be related, but might just be coincidental?
I am biased, tend to think infection first...
btw, she's VERY pretty