Let me start by offering my condolences for the loss of your dog at such a young age and having been through such a difficult time. Unfortunately, without knowing the specifics of what the symptoms and findings were with your pet, I can only offer some general thoughts. The vast majority of routine skin infections are easily managed with common antibiotics. The crusts and scabs that you describe are typical of staph bacterial infections; however, the failure to respond to therapy and what sounds like a dramatic progression of more serious symptoms does not.
The distended abdomen you describe and the soft, fluid-like appearance leads me to believe that multiple organ systems may have been involved and liver failure would be high on the list of considerations. A rare condition called hepatocutaneous syndrome may have been the source of your pet’s troubles. Liver failure can have a very insidious progression and you may not be aware of the loss of liver function. Some people may notice an increase in thirst or vomiting, but often no major symptoms are present. The end stage disease results in a sudden accumulation of fluid in the abdomen from the body’s inability to produce a major blood protein that helps keep liquid in the bloodstream.