The parents called 911 for help.
But instead of assisting, "police ended up putting a bullet in her," they said in a statement issued by the family's attorney.
Auburn police said Melissa Boarts charged at them with an unidentified weapon Sunday, prompting an officer to open fire and kill her.
Now the family is pursuing legal action.
Julian McPhillips, the attorney for the family, told The Washington Post on Tuesday that the parents believe Boarts may have had a pocket knife - "but certainly no gun" - and argued that shooting her was "totally unjustified."
"They are all deeply mourning and deeply hurt," McPhillips said of her family.
Boarts is one of at least 262 people who have been fatally shot by police so far in 2016, according to a Washington Post database. At least 41 of those killed by police were carrying a knife or other blade, and about a quarter of all police shooting victims were mentally ill or experiencing an emotional crisis.
People with untreated mental illness are 16 times as likely to be killed during a police encounter as other civilians approached or stopped by law enforcement, according to a study from the Treatment Advocacy Center.
McPhillips said the Boarts family intends to pursue the case "very vigorously," demanding dash-camera and body-camera footage from the scene.
"It's difficult to get true justice," he said, "because you can't bring somebody back to life."
After Melissa Boarts disappeared Sunday, her mother went looking for her, with her 2-year-old granddaughter in tow.
"We were able to find out she was headed on the interstate going to Auburn," Terry Boarts told the Montgomery Advertiser. "She was threatening to slit her wrists with a knife."
Terry Boarts told the newspaper that she called police and told them her daughter was "having mental issues - that she was bipolar, that she had been really depressed, that she was saying she was going to cut her wrists."
She said she told the authorities that her daughter had a knife.
Auburn police said officers responded at about 3:40 p.m. to a call about a suicidal motorist on Interstate 85 and followed the vehicle until the driver stopped on Red Creek Road in Macon County.
Police said she "exited the vehicle armed with a weapon and charged the officers in a threatening manner at which time the officers discharged their weapons, striking the driver."
The Macon County Coroner told AL.com that Boarts died from a single gunshot wound.
Police vehicles, a helicopter and ambulances swarmed the scene, according to reports.
The Boarts family told the Montgomery Advertiser they were informed there had been a fatality.
"We're still assuming the road ended and she hit a tree," Terry Boarts told the newspaper. "They never told us she had been shot."
The woman's twin sister, Melinda Boarts, said police finally came back and said "they shot her."
Her father, Michael Boarts, who worked 25 years as an officer for the Alabama Department of Corrections, said it was "absolutely outrageous."
"There was absolutely no justification for it and we are all in deep mourning," Michael Boarts said in the statement through the family's attorney.
Since January 2015, The Post has tracked more than 1,100 fatal shootings by on-duty police officers, with one in four involving someone who was either in the midst of a mental health crisis or was explicitly suicidal. A Post analysis has found that in half of those cases, the officers involved were not properly trained to deal with the mentally ill - and in many cases, officers responded with tactics that quickly made a volatile situation even more dangerous.
Auburn police called it a "tragedy for the Boarts family as well as the officers involved."
"Officers within the Auburn Police Division have encountered thousands of situations involving those with weapons or individuals intending to harm themselves," police said in a statement. "It has been nearly 40 years since an Auburn Police Officer was required to use force that ended in the death of another. It is unfortunate when someone intends to harm themselves and involves law enforcement to do so.
"Officers within the Auburn Police Division are trained to deal with disturbed individuals and have experience in doing so."
The State Bureau of Investigations, Macon County Sheriff's Department and Macon County Coroner's Office are investigating the incident, according to news reports. Findings will be released to the Macon County District Attorney.
Where to get help:
• Lifeline: 0800 543 354 (available 24/7)
• Suicide Crisis Helpline: 0508 828 865 (0508 TAUTOKO) (available 24/7)
• Youth services: (06) 3555 906
• Youthline: 0800 376 633
• Kidsline: 0800 543 754 (available 24/7)
• Whatsup: 0800 942 8787 (1pm to 11pm)
• The Word
• Depression helpline: 0800 111 757 (available 24/7)
• Rainbow Youth: (09) 376 4155
• CASPER Suicide Prevention
If it is an emergency and you feel like you or someone else is at risk, call 111.
