It happened around 9 p.m. at the Willow Green Apartment Homes on Willow Place Drive and Misty Willow Drive in northwest Houston near the Willowbrook area.
Detectives said 29-year-old Ericka Nicole McDonald broke in through a window and attacked her 51-year-old mother, identified in court records as Terri Mendoza, and her 63-year-old aunt in the apartment.
Family members provided these two photos of Mendoza, who was known as "Mimi."
Police said McDonald got into an argument with both her mom and aunt prior to the attack.
A witness who spoke with ABC13 on Tuesday said McDonald could be seen performing CPR on Mendoza moments after the stabbing.
McDonald took off after the attack, according to investigators, but returned to the apartment and told investigators she wasn't involved.
Police said McDonald was wearing a mask during the attack, but the aunt was still able to identify her. Clothes covered in blood were later found in McDonald's apartment, according to investigators.
Houston police said Mendoza died at the hospital. Family members said the aunt suffered six stab wounds during the altercation. She also required surgery, but is expected to be OK.
Prior to the attack, relatives told ABC13 they tried to get officers to intervene before things took a twisted turn.
Officers tried to take McDonald into custody on another charge just hours prior to the attack, but the Harris County District Attorney's Office declined to move forward.
The Houston Police Department says they received two calls of service on Monday for the apartment home. One was a disturbance call that came in around 3 p.m. and then a welfare check call came in just 30 minutes later. According to neighbors, McDonald, her children and Mendoza all lived upstairs, but in different apartments.
Police said the responding officer suggested McDonald be arrested on child endangerment and assault charges. The district attorney's office told ABC13 its prosecutors declined, saying they need more evidence.
The fatal stabbing took place less than six hours later, according to police.
McDonald has been charged with murder and aggravated assault with a deadly weapon. She's expected to make her first court appearance Tuesday night.