How can I pursue a sue case against a former employer for Defamation?

I'm in need of some advice. I'm trying to pursue a sue case regarding Defamation. I was denied employment from the job of my dreams by my former employer who had provide false information. I had the employer mail me out a copy of the background check, and one of my former employers thought it would be a brilliant idea to slander my character by stating my work performance was terrible. She provide them information stating I was hired as a bookkeeper rather than a medical receptionist and let me go after 3 weeks of trying to train me. But that's not true because I've keep all her emails with hours I worked which is more than 3 weeks, a dispute both she and I had because she never provided a W2, and money she owed me after I voluntarily left job. Proof of position, my resume including my qualifications, and references. May I add, on numerous attempts she tried to request me through LinkedIn. I can also provide proof of recommendation she kindly accepted and provided to my former employer