According to her obituary, Tesich was born in Winston-Salem, North Carolina in 1956, and moved with her parents to New York City in 1960, graduating summa cum laude with a Bachelor of Science in Psychology from New York University in 1976.
After graduation she moved to Boston, where she worked as a counselor for various psychiatric hospitals, specializing in counseling autistic children and their parents. In 1974, Sylvia began a life-long association with local police departments, assisting with solving missing persons cases. Her empathic powers helped find dozens of missing persons in New York City, Boston, and across New England.
She later worked for a covert government project in remote viewing alongside Reg Granowitz and Monty. They were joined by Johnny Smith for a operation intent on psychically tracking Al Qaeda militants in Pakistan, and the four successfully negotiated a squad of American soldiers out of an ambush.
On 27 november 2004, Tesich and Bonnie Gibson fled from the government program they were working for when they discovered a link between the project and the death of Senator Theodore Marshall. On the run, Tesich crashed her car and died on impact; Gibson survived the crash and fled, contacting Johnny Smith. Tesich was cremated on 30 November 2004, and her ashes were later spread near Lake Willoughby, New York.
Tesich was portrayed by Karin Konoval.