Sumiko, did she ever produce a document from a vet? I'm curious if she ever brought the little guy. That poor chinchilla, whether it died from a genetic defect or an owner defect. I think even if a vet told me it was genetic (which they would only be able to guess from listening to observations of symptoms, not really a firm diagnosis at all) it would bring me pause if my chinchillla ran into a wall and plopped over dead and make me wonder if I may have done something. As a responsible owner, I wouldn't even be able to own a chin immediately after--I'd have to deal with the loss and figure out if I could have done something different.
The fact that she isn't worried about her competence as an owner makes me worry about her competence as an owner...