Pascale Cécile Véronique Ferrier of Laval, Quebec, could face five years in prison and a fine of up to $250,000 if found guilty.
According to the criminal complaint, Ferrier addressed the envelope to Trump, but it was intercepted Friday by Secret Service agents at an off-site facility that sorts and checks White House mail.
In the letter, the complaint states, Ferrier demanded that the president "remove [his] application for this election."
"I made a 'Special Gift' for you to make a decision," Ferrier allegedly wrote, apparently referring to the ricin. "This gift is in the letter. If it doesn't work, I'll find better recipe for another poison, or I might use my gun when I'll be able to come. Enjoy!"
The complaint also identifies a now-deleted Twitter account that posted two anti-Trump tweets last month, including one that called for the president's assassination, as belonging to Ferrier.
An archived record shows that on Sept. 9, the account appears to have replied in agreement to an account asking someone to "shoot trump in the face" using the hashtag #killtrump.
The complaint also alleges that Ferrier sent six similar letters containing ricin to Texas law enforcement officials "addressed to individuals affiliated with facilities at which [she] had been housed while incarcerated in Texas in 2019." All seven of the letters contained similar language and were signed by "FREE REBEL SPIRIT."
Court records indicate that Ferrier was arrested in Hidalgo County, Texas, in March 2019 and charged with weapons possession and tampering with government documents.
CBC News reported Tuesday that Ferrier spent 20 days in jail and was released into the custody of Immigration and Customs Enforcement.
In a tweet Monday, Hidalgo County Sheriff J.E. “Eddie” Guerra said he and three other law enforcement officers had received ricin-filled envelopes.
Ferrier was taken into custody while attempting to cross the border from Canada into the United States on Sunday.
According to the complaint, she referenced that she was wanted by the FBI in connection with "the ricin letters" and was in possession of a loaded firearm and a knife.
She was denied bail and will remain in federal custody in New York until she can be transported to Washington, DC, for her trial.