Shannon Guess Richardson, 36, asked for a shorter sentence during a two-hour hearing in federal court in Texarkana. The 18-year term was set by an agreement when she pleaded guilty in December.
Richardson, a sometime actress, admitted sending two ricin letters. Ricin is a deadly poison made from the seeds of the castor oil plant.
One of the letters was sent to Obama and the other to then-New York Mayor Michael Bloomberg.
"I never intended for anybody to be hurt," Richardson said. "I do love my country, and I respect my president."
Richardson was also ordered to pay $367,000 in restitution and to spend five years on supervised release when she completes her prison sentence.
According to her IMDB entry, Richardson had small roles in The Vampire Diaries, The Blind Side, and the television series The Walking Dead.