She was not a teacher, as some media had previously reported, the friend added.
Despite whatever problems Nancy Lanza might have been facing behind closed doors, on the outside she kept a cheerful face. Several people who knew her said she was incredibly social and warm.
Several nights a week, she got take-out from the My Place bar in Newtown.
CNN sat down with owners Louise, Mark and John Tambascio.
Louise recalled Nancy starting a conversation with her, and how they become fast friends.
"She's funny. We took to her," said Mark Tambascio. "She did a lot in town and was always on the go."
Louise Tambascio said Nancy Lanza worked in charities for people with AIDS, and said she was extremely generous.
Louise saw Nancy Lanza take out her checkbook and write checks to anyone who told her they were going through a rough time and needed money.
"She was very kind," Louise said.
Lanza was generally in a good mood, several people said.
"Every time I saw her, she was so giddy and happy," said Amanda D'Ambrose, 23, Alan Diaz's sister.
D'Ambrose also knew Adam, and knew that Nancy owned guns.
"She was very responsible. She transported them safely. It wasn't something she boasted about," D'Ambrose told CNN.
Yet when she heard the news that there had been a shooting at Sandy Hook Elementary, D'Ambrose started calling Nancy Lanza's cell phone.
As the young woman recalls this terrible moment, she weeps. I was "hoping it wasn't true," she said.
Nancy Lanza's guns
The three weapons found at the scene of the shooting were legally purchased by Nancy Lanza, a law enforcement official familiar with the investigation told CNN.
The Bureau of Alcohol, Tobacco, Firearms and Explosives is investigating the school shooting.
CNN confirmed Monday afternoon with ATF that Adam Lanza and his mother frequented several gun ranges over the past several years. The agency will not identify which ranges.
Russ Hanoman, a friend of Nancy Lanza, said she was the "epitome of responsibility."
"They've painted her as some irresponsible gun freak, but she wasn't," he said. "She was a paragon for gun safety. She taught the boys how to use the guns responsibly."
Police Chief Donald Briggs Jr. said he, too, knew Nancy Lanza.
"She was a great person who would do anything for you, a heart of gold," he told the Union Leader newspaper.
"She was just a real, real nice, nice person."
Alan Diaz keeps asking the same question everyone is: How could this person he knew, who seemed a little off, kill children?