DALLAS » A Texas woman and former actress pleaded guilty today to sending ricin-laced letters to President Barack Obama and New York Mayor Michael Bloomberg, under a deal that her attorney has said would cap prison time at 18 years.

Shannon Guess Richardson entered her plea in federal court in Texarkana, Texas, to a federal charge of possessing and producing a biological toxin.

Richardson was arrested in June after authorities said she tried to implicate her estranged husband, Nathan Richardson, after he had filed for divorce. Prosecutors say Shannon Richardson mailed three letters from New Boston, outside Texarkana, then went to police and claimed that her husband had done it.

Richardson, 35, has had minor roles in the television series "The Walking Dead" and the movie "The Blind Side." She also is the mother of six children — including one child born prematurely while she was in custody this year.

Prosecutors say investigators noted inconsistencies in Richardson’s statements and later learned that she had purchased materials online to produce ricin, a toxin that can cause respiratory failure if inhaled.

She acknowledged in a signed plea agreement document filed today that she ordered castor beans online and learned how to process them into a substance used to make ricin. She obtained an email address, a PayPal shopping account and a post office box in her husband’s name without his knowledge, according to the document.

On the morning of May 20, she said, she waited for Nathan Richardson to go to work.

"After he left the house, I printed the mailing labels for President Barack Obama, New York City Mayor Michael Bloomberg, and Mark Glaze with The Raben Group," Richardson said in the document. Glaze is director of Mayors Against Illegal Guns, Bloomberg’s group advocating for tougher gun control.

The letter to Obama, according to the document, read: "What’s in this letter is nothing compared to what ive got in store for you mr president."

"You will have to kill me and my family before you get my guns," the letter read. "Anyone wants to come to my house will get shot in the face."

After mailing the letters, she admitted to trying to blame her husband and lying to authorities.

Her attorney, Tonda Curry, said last month that she and prosecutors agreed to a deal capping Richardson’s sentence at 18 years. Prosecutors say Richardson faces life in prison for the charge to which she pleaded guilty.

Curry has said that Richardson wanted to "tell the government who else was involved in those offenses," but declined to name anyone. In the document filed today, known as a factual resume, Richardson does not name anyone else but says that the supplies she ordered "were used to make ricin" — not that she made the ricin herself.

Nathan Richardson has not been charged in the case, even though Shannon Richardson has repeatedly tried to blame him, said John Delk, Nathan Richardson’s attorney.

"He was interviewed the very first day, and he’s been cooperative since Day One," Delk said.

Nathan Richardson has temporary custody of the couple’s newborn son, who is healthy and steadily growing, Delk said. The couple’s divorce likely will not be finalized until next year.

A federal judge ultimately will sentence Shannon Richardson at a later sentencing hearing, which has not yet been scheduled.