Wendy Lin (Amy Acker) was a technician in the Chem Department, responsible for chemically altering the five college students in order for them to better fit their roles.
In the beginning of the film, she informs Hadley and Sitterson that the Stockholm branch has failed. They inform her that the last time things went wrong in the American branch, it was fault of the Chem Department. She helps explain how things work in the ritual to Daniel Truman, who is new to the facility.
After it is revealed that Marty is still alive, she figures out that somehow it was his stash of marijuana that kept him immune to the drugs.
Wendy Lin is played by Joss Whedon staple Amy Acker, who has previously played Winifred Burkle on Angel and Dr. Claire Saunders on Dollhouse.