For those of you who think that random managers can just make up company policy or contract language whenever they want (which almost everyone seems to think they can), read the company's "our people" policy. And foul language is not a firable offense, the union recognizes that we are human beings (even if the company does not) and that things can get heated. A good supervisor in that situation would have asked what the problem was, and either tried to find a solution, or asked her to take 10 minutes to cool off.
Any manager who tries to have an employee fired for insubordination probably deserved the insubordination, is probably lying or exaggerating the circumstances, and is most likely completely unqualified for their job.