You're arguing against a straw man. If she felt she was worth more than the salary she was offered, she shouldn't have accepted it in the first place. Simple as that.

Who can say what was going on in the inner world of this hypothetical second-hand story person's mind?

All we know is she took a job and then took a better one.

You're claiming that's an unethical act, and I'm saying, "it's the free market, baby!" They pushed for at-will, they got it, consequences and all.

And, more broadly, I grew up in the transitionary period from "one job for life" to "throw 'em to the wolves," and I have absolutely zero sympathy for employers, in this world their policies have wrought.

There's a local employer here that is a household name. They have a history of doing things like offering positions to entire teams of people and then laying them off before their first day at work. In spite of the fact that they are one of the largest employers in the area I refuse to work with them because of their unethical behavior. Just because there are not laws which ban unethical behavior does not mean there are no consequences. I'd generally rather not work with someone who has shown a history of quitting after 3 weeks.