Yeah I'm not understanding the "Right to Work" discussion here, as this doesn't involve unions.
At-will employment applies here (as Gordman stated), allowing Cracker Barrel to terminate Brad's wife for any reason that isn't discriminatory or against the law.
There are a few other protections that at-will employees have, such as protections against being fired for refusing to commit illegal acts, taking family/medical leave, or engaging in certain protected legal actions (such as testifying in someone else's wrongful termination case).
Bottom line is that poor Brad's wife isn't in good legal standing, though I think the employment doors will be wide open for her after this.