The potentially deadly ricin, federal agents allege, was homemade by the 70-year-old to go into the food and drink of her neighbors at a Vermont continuing care retirement community.
Earlier this week, the FBI was asked to come to the Wake Robin life care community in Shelburne, Vermont, to investigate a potentially toxic substance.
When an agent interviewed Miller, she allegedly told him she was making ricin in her home and testing its effectiveness on other residents of Wake Robin.
"On at least three occasions, Miller exposed other residents to the ricin she had produced by placing it on food and/or in beverages she expected them to ingest," Special Agent Mark Emmons wrote in a criminal complaint.
Miller indicated she planned to take the ricin herself one day, Emmons wrote.
The FBI searched her home and in the kitchen found a wicker basket that had pill bottles with various writings on the labels. A bottle labeled "ricin" was half full with a yellowish white powder, which tests later confirmed was ricin, the complaint says.
Miller was arrested and charged with unregistered possession of a select agent. She made her initial court appearance Friday.
CNN was unable to reach the public defender who represented her. A spokesman for the US attorney's office told CNN she actually is not eligible for a public defender and will need new counsel for her probable cause and detention hearing on Wednesday. It is unclear whether Miller, who is in custody, has hired a new attorney.
No residents reported symptoms consistent with ricin poison, the complaint says. Authorities said the potential threat was limited to Miller's home and has been eliminated.
The retirement community owner said it notified local authorities when they were alerted to the situation. A statement from the president and chief executive officer of Wake Robin did not disclose how the community staff became aware of the potential threat.
"The safety and security of Wake Robin residents and staff are ALWAYS our highest priority," Patrick McKee said in a statement. "This was an isolated incident. The toxic substance was contained; no residents were evacuated."
Ricin is a deadly toxin derived from castor beans and has no known antidote.
It can be used in powder, pellet, mist or acid form.
If enough is ingested it can cause nausea, vomiting and internal bleeding of the stomach and intestines, followed by failure of the liver, spleen and kidneys, and death by collapse of the circulatory system.