Everyone in the chain of command who thought that disciplining her over this is the correct course of action, should be fired. Her manager for threatening to terminate her should be immediately terminated.
It’s long past the time where I would be in any legal jeopardy for doing so, but I do it from respect.
That company had pretty strict HR policies, and one of them, was that a manager could never mention any disciplinary outcomes to employees. That was a privilege reserved only to HR. A manager could only mention that a matter may be referred to HR.