She doesn’t mention the write characteristics of the system but she implies that it was pretty write heavy.

In that case it’s not obvious to me that putting a key prefix index on every column is the correct thing to do, because that will get toilsome very quick in high write loads.

Given that she herself wrote the before and after systems 20 years ago and that the story was more about everyone having dumb mistakes when they are inexperienced perhaps we should assume the best about her second design?