In a situation where you're fired for refusing to carry out your boss's instructions, it's pretty reasonable to assume that your replacement will be selected, in part at least, on their willingness to do what you would not.
Having that opinion is very different than publicly calling them liars before they've even had a chance to step into the role. Whatever else we ultimately find out about this, it is clear on its face that this act was unprofessional (and to me, destroys her credibility).
How very different is it when the order that was refused to be carried out was lying? In this scenario, someone was fired for effectively not lying. For that person to then make the claim that one could reasonably expect their successor to do the lying they were unwilling to carry out is only logical if they wanted to keep the job. Sure, perhaps calling them "liars" is harsh diction. But what's unprofessional is firing an employee because of their integrity in regards to the truth, especially pertaining to public safety
There are no perfect whistleblowers. If you're looking for something that destroys their credibility, you'll always be able to find one. Your particular complaint here is purely aesthetic and I think we'd all be better off focusing on the substance rather than going ten rounds about word choice and tone.