Season 4, episode 2, starting around 5:42 mark:
She passed away in 2013. A YouTube commenter notes:
Mrs. Shiono (the lovely origami lady in this video), was my grandmother, who sadly passed away a few years ago. As you can tell from the video, she was an incredible origami artist and was still folding til the end. The fact that she had been on Mister Rogers' was a little fun fact my family loved to share: I still remember freaking out when this episode re-ran on our PBS station one time. She would be happy to know this episode made an impression on so many of you in the comments, when you were watching it on TV and even watching it now so many years later.
I haven't seen the recent Mr. Rogers documentary movie, but I've only heard great things about it.