The general principle is that you shouldn't be able to "sign away" something that's a constitutional or human right. Like the right to freely speak, the right to practice a religion, the right to be paid for work, and so on. Imagine if the severance contract specified that she had to convert to Islam in order to get her severance, or that she had to sacrifice a child. No court in the country would consider those clauses conscionable. Yet, somehow companies are allowed to gag your free speech as a condition in a contract? It makes no sense why this is allowed.