Suing for Slander in Texas?

After a verbal disagreement stemming from an ongoing feud with our apartment manager she called my husbands job and told the supervisor of the safety department that he was "on so much dope I don't know how he holds up a job." My husband works 6 days a week most of the time and sometimes working up to 70 hours a week as a pressure testing technician. He works out of town sometimes and drives a company truck. All of this has been put in jeopardy because of this woman's phone call. He isn't allowed to drive a company truck pending a drug test. This happened on a Thursday evening and by Friday morning at work everybody knew about it. During the phone call, the woman was put on speakerphone so multiple people in the office heard what she said. While this was the reason that the whole company knew, I figured it would help our case that more than one person heard her say it. How would we go about filing a lawsuit? Would we file it against the apartment manager herself or the company that she works for? How much could we sue for? What is the statue of limitations? We live in Harris County, Texas so would it be better to hire a lawyer or should he try & represent himself? Would a lawyer take this case pro-bono?