Well, no-one buzzed her during the half mile I was behind her, versus multiple cars buzzing her both before and after I was behind her, so I doubt I actually made her situation "worse".

Anyway, it would have been hard to pass her without buzzing (passing very close). Once I got slowed down to 10 mph, then was a stream of cars whistling by me on the left; I would have had to get a gap behind her, then accelerate pretty briskly to merge.

Next time, I guess I'll blow by her like everyone else was doing, without letting myself get slowed down. I think this time, I was so taken aback that I kind of slowed down in amazement.

I wonder if I did make her uncomfortable? I'm not sure she even knew what was behind her. She never looked back, and had no mirror. I think - not positive - that she was simply poking along, oblivious and/or counting on all the cagers being as well-trained as spare_wheel thinks they are.

Indeed, Portland drivers are well behaved for - the most part. But not nearly all are. We have a steady enough stream of bicyclists being hit, as proof of that.