Redstone's attorney Gabrielle Vidal told Reuters the lawsuit was baseless.
"It is a meritless action, riddled with lies, and a despicable invasion of his privacy. It proves only that Ms. Herzer will stop at nothing to pursue her personal financial agenda," Vidal said. "Herzer's claim that she filed this lawsuit out of concern for Mr. Redstone is preposterous."
Redstone's physical and mental health have been the subject of intense debate and speculation, in part because the mogul has been largely absent from his companies' earnings calls lately, whereas he previously kicked off the calls with lavish praise for his executives.
Redstone controls about 80 percent of the voting shares in CBS and Viacom through a holding company, National Amusements.
Herzer had been chosen by Redstone to make healthcare decisions for him in case he was not able to, the lawsuit says, until Redstone executed a new agreement on Oct. 16 to remove Herzer as his health care agent.