She was portrayed by the late Lorena Gale.
Following Lex Luthor's return to civilization after being stranded alone on an abandoned island, Foster was hired by Lionel Luthor to provide Lex with psychiatric care. Dr. Foster was mentioned by name as the psychiatrist with whom Lex would meet with.
Lex had met with Dr. Foster four times and was finishing up his last session with her, talking about the art in the castle and claimed that he had no emotional issues. Dr. Foster refused to sign off on Lex's mental health, recommending continuing sessions on an indefinite basis.
Much to Lex's fury, she maintained that he has yet to deal with any of his emotional or physical trauma. Lex seemed to know that she was right, but he is still upset and threw her out. After an outburst towards Perry White, Lex agreed to more sessions.
Lex told Claire of his time on the island and of the apparition of Louis Leery that tormented him during his isolation. Doctor Foster promised that their sessions were confidential , but called Lionel to inform him of her discovery.
Seeing as he was close to discovering the truth about his grandparents, Lionel paid Dr. Foster to drug Lex until he seemed to be having a psychotic break. When Lex believed assassins were after him, Clark and he returned to the mansion to search for clues, only to discover his bodyguard Darius was alive.
When Dr. Foster arrived, she tried to convince Lex that he was having a psychotic break.
Lex refused to believe her and grabbed a gun and backed out admitting that he might be crazy, but he has also guessed that his father might have drugged him in order to discredit him.
Lex went to confront Morgan Edge and when he was almost ran over, Clark pushed Lex out of the way and destroys the car, with Lex witnessing his powers. Clark super speeds away just as Dr. Foster arrives with some men who haul Lex away as he screams for Clark and what he's done.
Dr. Foster had Lex committed to Belle Reve Sanitarium where she continued a drug regime designed to erase his short term memory. He is unhappy that his son has been in in Belle Reve for an entire month with no results.
After a month, Lex still hadn't forgotten, so Lionel insisted that Dr. Foster administer radical shock therapy. She was reluctant as she had other patients who were badly injured during the treatment.
Clark and Chloe Sullivan did research at the Torch about Lex's treatment. He can't find anything conclusive, but he discovers that Lex has been recommended for radical electroshock therapy in twenty-four hours. They learn that Dr. Foster's last patient to receive the treatment is in a permanent vegetative state.
They corner Dr. Foster at Metropolis General with this news and accuse her of drugging Lex to make him delusional.
They warn her that she will be in great danger from Lionel if Lex becomes a vegetable and they beg her not to perform electroshock therapy on Lex. Clark told Pete that Dr. Foster was going to sign the cancellation papers on Lex's procedure.
She was killed in a car accident before she could cancel the order. Chloe reported her death and Pete suspected that Lionel had her killed.