How do you go about asking for a raise?

I made a comment in the weekly thread for some advice, feel free to read it for some more context if you want (warning it’s long).

What’s the process of asking for a raise? Should you go in with numbers and stats or act as if you don’t get a raise you’re going to leave and they will lose the business you bring in? A little bit of both?

My wife hasn’t had a raise in about 4 years. She makes $45k, is the sole employee of her satellite office with almost zero ‘overhead’ since she works entirely from home. She brings the company >$500,000 in revenue each year and if she were to suddenly quit the closest employee would be >200 miles away and it’d be extremely unlikely they’d make a new hire in the area so quickly since there’s essentially ZERO company presence in the area besides my wife.

How should she go about demanding a raise? She has a pretty low career self image and is non-confrontational. Is there some resources to 1. get an idea of what a realistic salary/revenue brought it could be? 2. way to improve her confidence or see that they’re taking advantage of her financially? 3. make a solid plan of what to say and how to act during a potential meeting with her boss about demanding a raise?

I’m at a loss and feel her self esteem and our families future is being held back by this.