"how do you think the Kathy Nguyen death fits into this?"
For me it was very suspect she worked in a medical/biological facility. But then, many people do.
Don't forget the old woman in Connecticut who got it. To me that's more anomalous, geograhically. Some mail cross-contamination theory seems more plausible for Nguyen, being she worked in Manhattan where some of the letters were sent.
I think Nguyen is the real anomaly, not Lundgren.
Lundgren was a frail 94-year-old woman. It's no surprise that a small number of spores might be sufficient to overcome her immune system. And, although they didn't find the actual piece of her mail that had contained anthrax, they did find that the USPS letter-processing machines that processed her mail were heavily contaminated. I think they also found some anthrax spores on a piece of mail at one of her neighbor's.
In contrast, Nguyen was only 61 years old, still healthy and working. Yet she succumbed so quickly that she was unable to speak with investigators at all. There were no anthrax spores at all found in her neighborhood or in the places she frequented, in spite of being scoured for evidence.
Another contrast is that Lundgren had led an ordinary life, while Nguyen had a colorful background.
I think Lundgren was just a very unfortunate old lady, while Nguyen's case is truly an anomaly. And any anomaly is a clue.