There is also the matter that, according to the plaintiffs, she was paid (indirectly through her husband's estate) and contractually bound to keep her mouth shut.
Contracts don't work indirectly like that. Either you agree to the terms directly or you don't. As all legal organizations including the SCOTUS recognized, a valid contract requires free consent.
Either she was a party to the contract with it's nondisparagement clause, and agreed to keep her mouth shut about all production details, or she was not part of the contract and the company is in the wrong. Her statement was that the show made during her husband's life and with her husband's contract was done "without my knowledge or cooperation," which is quite likely since her then-living husband likely took care of his own business deals.
Some portions of a contract may survive a death and transfer to estates. Others automatically dissolve completely (such as partnership agreements between two people) or require affirmation that the new parties accept the new terms of a new, successor agreement. Binding nondisparagement terms do not transfer to other people.
On its face it looks like the company made an agreement with a now deceased individual. The question is one of contract law. If she signed the contract then she was bound and shouldn't have said anything. But if she didn't sign the agreements, she should be adding a counter-claim.
Can they produce such a contract? Do they have a nondisparagement agreement that SHE signed? That's the key to the entire dispute.