The woman told London's Southwark Crown Court the defendant knew she was living in care after being sexually abused by her father but went on to make her perform a sexual act.
She said she went to his offices in 1988 as she had heard he could help her become a model, and when she met him he told her of a potential film role.
The woman, now aged 42, said the second time she went to his offices he told her she needed to talk to the film's director to "audition" and directed her to a department store and answer a public telephone. She said a man called who said he was the director. He told her to return to Mr Clifford's office and find his "Achilles' heel".
She told jurors that when she returned to his offices, he exposed himself to her before telling her to return to the phone box at the store.
During the second conversation with the purported director, he told her to return to Clifford's office and find his "weakness".
She said the defendant exposed himself to her, before making her perform a sex act. Mr Clifford, from Hersham in Surrey, denies 11 counts of indecent assault.
The trial continues.