Then the going rate for what she does is half what she is making. If others will only pay her half her current pay then that is what she is worth. That means for her to earn what she is earning now by working elsewhere, she would need to have two full time jobs. That would mean working 80 hours a week.
Perhaps she should tell that to her boss that other employers would only pay her half what she is now making. He could then lay her off, and hire one full time and one one part time worker to replace her for about 60 percent of what he is paying to get the job done now.
Workers always think the company has this big pile of money they could pay them if they just were not so greedy. Then they wake up one morning to find the company is broke and they don't have a job.
The business cycle has never been repealed. There are good times and bad times. Workers had best figure ways to help keep the company afloat.