Shannon Guess Richardson was charged Friday with mailing a threat to the president. The federal charge carries up to 10 years in prison.
The 35-year-old actress and pregnant mother of five contacted authorities on May 30 to implicate her husband.
An FBI affidavit says she failed a polygraph test and investigators found inconsistencies in her story.
The affidavit says she later admitted mailing the letters knowing they contained ricin, but said her husband typed them and made her do it.
No charges have been filed against her husband. His attorney says the couple is divorcing and the letters were a setup.
