what is a scenario where the employee would have leverage in a layoff? it’s hard to imagine except if something unethical/wrongful was going on leading up the layoff: sexual harassment, discrimination
There is a good chance someone would even pay her for that information, so she has leverage by saying "you're going to cut off my future income, how much is that worth to you?".
Or a situation where there was some questionable behavior and there could be a lawsuit about wrongful termination. Usually the severance comes with a waiver where you waive your right to sue the company. So it's a negotiation of how much that waiver is worth to both you and the company. The higher up you are, the more likely there is room for negotiation there on the value of a possible lawsuit.