Sharlotte Hydorn, a retired public school science teacher from Spokane, Wash., pleaded guilty to a tax charge dating back to 2007.
Under a plea agreement, Hydorn was sentenced to five years' probation and a $1,000 fine.
She was also ordered to stop selling the kits and advising people on how to commit suicide.
It will be up to the IRS to determine how much money Hydorn owes in back taxes.
Federal agents raided Hydorn's home in May 2011, seizing a computer and three boxes of material.
Hydorn sold her product for $40 under the name "GLADD Group."
It consisted of a plastic hood that closes around the neck, along with tubing that connects the hood to a tank of helium or other inert gas, which the purchaser had to provide.
Hydorn began assisting physicians with patient suicides after her husband, Rex, died of colon cancer, her attorney, Charles Goldberg, said.
Her husband was in pain and didn't want to die in a hospital hooked up to tubes, Goldberg said.
Hydorn has said her so-called "exit kits" were intended to help terminally ill people end their lives with dignity in their own homes.
But prosecutors said she took no steps to verify the identity, age, physical condition or mental state of her customers.
She therefore had no idea if the kits were being bought by people suffering from depression or minors acting without adult consent, they argued.
Court documents say she sold more than 1,300 kits to people across the United States and abroad.
Investigators determined that the kits were sold to at least 50 people in San Diego County since 2007.
Four of those people used the kits to commit suicide last year. None was terminally ill, according to investigators.
Hydorn admitted in court that she made $66,717 in 2010 and paid no taxes on that.
She has been allowed to remain free on $10,000 bond on the condition she not assist any suicides.