No. There is no law that makes what they did a crime. They were talking among themselves in a conversation that they evidently did not mean for your wife to overhear. But even had they insulted her to her face there would be no crime. The First Amendment protects the right to free speech, even when that speech is offensive or insulting. Nor is there any civil lawsuit here. There is nothing to sue over being offended by what someone else says to you. The complaint to the employer is really all you could on this.

