Arizona police said Blessing's 72-year-old son was found dead on Monday at his home in Fountain Hills, located about 50 kilometres northeast of Phoenix.
The man's name wasn't immediately released.
Blessing had been living with her son and his girlfriend for about six months, according to court records, and the elderly woman had reportedly become worried that the pair were plotting to move her into a home.
She told authorities that she argued with her son on Monday morning over the way she was being treated and was upset with him for stating that he was going to put her in a nursing home.
Blessing told police she got out two guns, which she said she has had since the 1970s — one bought at a gun store and the other obtained from her late husband. She told police she hadn't fired either since the 1970s.
She concealed two pistols in the pockets of her bathrobe before confronting her son in his bedroom and firing multiple shots at him with one handgun, records show.
She reportedly turned the gun on her son's 57-year-old girlfriend but after a struggle the woman was able to wrestle it out of her hands.
She also managed to get the second gun away from the 92-year-old.
The unidentified woman called authorities and Blessing was located on a recliner in the home and taken into custody.
Blessing told police she had wanted to kill herself but was out of weapons.
When detectives asked her what she thought should happen to her she replied she "should be put to sleep as a result of her actions".
Sheriff Paul Penzone said police had been called out to at least one other case of domestic violence involving Blessing and her son but could not give further details.
"It is always concerning when domestic issues escalate to violence or tragic outcomes," Penzone told a local TV station. "They are often isolated and neither predictable nor preventable."
