Whenever money is involved in a crime, whoever benefits most should be suspected first. Homo sapiens are so addicted to material wealth that they still do bad things to get it even if they don’t really need it. Ever since there is written history, money and wealth probably is the top motive under which crimes are committed.
This is almost cliche, and exactly what happened here. Holmes pretty much solved the case as he was listening the lady telling the story. And the deductive details of her being short sighted and a typist were merely fancy steps in the middle connecting the dots.
Financial motive made the crime in this story feel petty (killing for love, on the other hand, does feel more romantic and larger than life…), and cheating a closely related young lady out of her innocent love made it despicable. But I guess I have to say I have seen far worse in real life.