Dana Miller was an employee of Virtanen Pharmaceuticals who worked in clinical trials.
She was killed on the orders of Mark Lawson and Robert Keller, because she was planning to blow the whistle on them when she found out that the company was faking FDA reports on the clinical trials of their newest drug, Sylocet, which could easily kill 30,000 people. Dana was transferred within the company five days before she was killed. According to the police report, Dana died of a brain aneurysm, but Reese figures that Lawson had her killed, presumably using drugs from the company.
She made a secret recording of her conversation with Lawson that found it's way to the hands of Anthony Talbott. Dana had appeared in a promotional video for Virtanen which allowed Finch to match her voice to the secret recording. Finch was able to confirm that the recording was made in Lawson's office. On it, Lawson calls up Keller and the CEO himself tells Dana that he knew all about the altered drug trial files.
Her number was produced by the Machine roughly 6 months before Harold Finch and Reese started to work together. Finch claimed that he "was not in a position to help her" since he didn't have Reese at the time. Fixer Zoe Morgan was hired to get Dana's recording from Talbot but made a copy before turning it over from which Finch was able to identify her. Finch eventually cleaned up the recording and discovered the true extent of the corruption, short selling Virtanen stock as a way of getting at Keller. Keller and Lawson were later arrested on charges of fraud, conspiracy and murder while Sylocet was shelved thanks to Finch, Reese and Zoe. Zoe tipped off Virtanen's competitors about what was about to happen, but donated most of the money she got for it to Dana's family for their civil suit against Virtanen while Finch was relieved to get justice for a number he was unable to save. (“The Fix”)
Keller was later found guilty of her murder, which led to charges being brought against Lawson. (“Risk”)