Brett was the newcomer under Dawson, but she eventually became the veteran.
She took Violet Mikami (Hanako Greensmith) under her wing, and they became such close friends that Violet was the Maid of Honor at her wedding. A wedding that effectively ended Brett’s time at 51.
The medic departed in season 12, as she decided to move to Oregon to live with her adopted daughter and her new husband, the aforementioned Matt Casey. We got a brief mention of Brett in the season 12 finale, though, so there’s still a chance she could return for a cameo.