Harnois was originally signed to guest star in the May 5 episode as the estranged daughter of Conrad Ecklie (Marc Vann), who works for the Los Angeles Police Department and helps the Las Vegas crew hunt down serial killer Nate Haskell (Bill Irwin).
The guest stint grew into a bigger role on the show. She was expected to return for more episodes and has now been upgraded to a full-blown regular.
CSI, now in its 11th season, has not been officially renewed for next season but that is considered a foregone conclusion. Harnois’ series credits include Point Pleasant, Dirt and One Tree Hill.