Dementia sufferer Laura Lundquist is suspected of killing Elizabeth Barrow in their room at the Brandon Woods Nursing Home, Massachusetts.
Barrow was found dead in bed with a plastic bag tied around her head.
It was first believed to be a suicide but Lundquist was arrested after an autopsy indicated her roommate had been strangled.
She was indicted on a second degree murder charge at a court on Friday and has been sent to a state mental hospital for a competency evaluation before her arraignment.
Her defence attorney, Carl Levin, said she has a "long-standing diagnosis of dementia, as well as issues of cognitive impairment."
The alleged victim’s son, Scott Barrow, claims Lundquist had complained about the number of visitors his mother received and had made threatening and harassing remarks to her.
The two women had been roommates for about a year, despite calls by Mr Barrow to separate them.
He said his mother told him she did not want to leave her room because she had previously shared it with her husband for several years before he died in 2007.
The day his mother died, Mr Barrow claims he saw Lundquist being wheeled away from the room.
Barrow said: "She said to me, 'You're going to blame me for this ... but you're wrong’."
District Attorney Sam Sutter said Lundquist suffered from paranoia and "harboured hostility toward the victim" and thought Barrow "was taking over the room they shared."
He said that Lundquist is believed to be the oldest murder defendant in state history.