Dr. Rachel Cranston (née Todd) is a psychologist and also the older sister of deceased former Secret Service/NCIS Special Agent Caitlin Todd.
Seven years after Kate's death, Rachel made her debut appearance in the Season Eight episode A Man Walks into a Bar (episode), as she wanted to evaluate Leroy Jethro Gibbs's team in order to "meet the people Caitlin worked with"; in doing so she found a measure of closure. During a talk with Gibbs, Rachel revealed that she hadn't been able to attend Kate's funeral at all.
At one time she resided in Miami, Florida.
Rachel never appeared (or was even mentioned) during the time Kate Todd was still alive and active on the team, but during the Season One episode The Good Samaritan (episode), Kate briefly mentioned that she had a sibling who was listed as her emergency contact and who also resided in Miami, which suggested that it might have been Rachel. She was mentioned once when Kate was talking to her on the phone before a case, but no name was given.