Well, if the bank had told her not to use that phrase, she certainly should have expected to be fired. The bank was well within its rights to tell its employees what to say or not say. However, it's also in my rights as a consumer not to use that bank if I disagree with its restrictive policy.
For the record, I don't actually believe there were legitimate complaints. I think the bank is making that part up.
As pointed out, the bank is contrary to federal law when it discriminates on the basis of age, sex, RELIGION, etc.
So, there is no right to harm.
Unless one is a disease-ridden queer, you can fire anyone for any reason. Of course you are correct when assuming that the bank is infested with liars trying to protect their public image. I hope the wealthy of KY pull their money from this bank.