After posting a $10,000 bond, she fled with her three children, including twin sons. She ended up in Georgia, where she worked as a waitress, raised her children and made new friends.
But she remained a fugitive and after more than four decades, cold case investigators tracked her down to her apartment in the small town of Lake Park, Ga., located in the southern part of the state near the border with Florida.
Now 76 years old and in bad health, including heart problems, Rivera was extradited back to Houston this week. Due to her health problems, Rivera could not be flown back to Texas. Authorities drove her back instead.
She is set to appear in court on Friday on a charge of murder by omission. She remained jailed without bond. Court records did not list an attorney for her.
When reached at his home in South Carolina, Mark Rivera, one of the elderly woman's sons, declined to comment.
According to court records, Rivera is accused of killing her husband by "throwing hot grease on him and by throwing other substances and liquids ...."
The court records did not give a motive for the alleged slaying. Donna Hawkins, a spokeswoman for the Harris County District Attorney's Office, declined to comment on a motive.
Hawkins said an investigator with her office's fugitive apprehension section had worked on the cold case for several months, first tracking down Rivera's sons and eventually finding her Georgia address.
Rivera's arrest shocked her friends and neighbors back in Georgia.
Lorraine Robertson, who knew Rivera for more than 25 years and lived in the same Georgia apartment complex, described her as a "real sweet person, loving, warm hearted."
"It was a shock to me when I heard about it," Robertson, 59, said. "I was like that's not Mary. She wouldn't do nothing like that."
Officials with the Lowndes County Sheriff's Office, which arrested Rivera in Georgia, said they were contacted by Houston police, who were looking for the elderly woman.
Robertson said investigators with the sheriff's office first spoke to Rivera at her apartment about six weeks ago, asking her questions about who she was and her husband.
"They asked her how (her husband) treated her. She said they got along, raised their kids," Robertson said. Rivera had indicated that her husband had slapped her once but "that was it," Robertson said.
Authorities said law enforcement was never called to the couple's Houston home on allegations of domestic violence.
Investigators in Georgia returned a month later and asked her similar questions.
Robertson said Rivera had previously not talked about her husband and told investigators that he had died and after his funeral she moved to Georgia.
Investigators returned a third time, on Oct. 11, and arrested Rivera.
"Me and another neighbor walked her out. I could feel her whole body trembling," Robertson said. "We put her in the car. She cried. We all cried with her."
Rivera was held in the Lowndes County Jail until she was returned to Houston late Wednesday.
Robertson questioned why Rivera was being arrested after so many years and now that she is frail and in bad health, including heart, back and breathing problems. Rivera has been hospitalized four or five times in recent years, she said.
Hawkins declined to comment on Rivera's health issues.
"The defendant was charged with committing a rather brutal murder of her husband. Although she was able to elude authorities for over 40 years, she ultimately must face judgment in a court of law for the murder of her husband," Hawkins said.