Jennira Roundtree was knifed multiple times in the chest around 7:30 p.m. Tuesday outside her building on Henderson Avenue near Alaska Street, part of NYCHA’s West Brighton Houses, authorities said.

She was trying to come to her daughter’s aid and took the brunt of the assault, according to the sources.A 30-year-old neighbor told the Daily News that a group of girls picked a fight with Roundtree’s 12-year-old daughter — prompting the mom to jump to her defense.

Roundtree’s friends had initially called the girl’s older sister for help, but the quick-acting mother got involved sooner, the neighbor said.

“Some girls come in to fight with the little girl and some friends, they go upstairs and then the sister was coming,” the neighbor said. “I don’t know where her mom came from. Maybe she was outside [already].”

The neighbor said she couldn’t fully see the mayhem because of scaffolding, but heard what happened. She ran downstairs and already saw officers taking the mortally wounded Roundtree away.

“The police took her,” she said. “When they carried her, I saw she had a lot of blood. I heard her say, ‘I can’t breathe!’ That’s the only thing she said.”

Roundtree was rushed to Richmond University Medical Center, where she was pronounced dead.About 20 people were involved in the melee, police said. Authorities confirmed that a daughter of the victim was on the scene, but was uncooperative.

No arrests have been made.

“This neighborhood was important to her because she wanted different for all the kids coming up,” one of Roundtree’s friends told WABC. “And she was trying to make a difference, and she was.”