Offhandedly mentioned (but not by name) as Kate's sister in Miami in season one, Cranston managed to get assigned psych eval duty on Gibbs' team just so she could meet Kate's coworkers. He also does the near-impossible by becoming actual friends with Gibbs, to the point where they have a biweekly racquetball match and chat on the phone almost daily.
At home, a single mother with a divorce from an abusive husband in the past.
Introduced in Season 15, a graduate student at the medical school in New York where Ducky is guest teaching, and stands out as a protege.
This budding friendship lets her make her way to the NCIS headquarters, where she proves herself highly valuable.
Her regrets follow her, and they truly left their mark.
She later transferred from the Southwest Field Office in San Diego to NCIS Headquarters at the behest of Director Vance, and is now the team's profiler and emotional crutch.