Sheriff's homicide detectives said the body was discovered about 9:30 a.m. inside a house she shared with her mother and children in the 39000 block Desert Holly Lane.
Detectives said they believe the murder happened overnight and that the woman's six children and mother were home when it happened.
Neighbors said they didn't see anything unusual Saturday night or early Sunday morning, and that they didn't hear anything either.
The victim's brother, Lovell Perry, says that when some of the children went to wake up their mother, they found their 1-year-old brother in bed next to her body.
"My nieces broke the door and they found her under the cover, face down, with the wound to her back," Perry said.
The family says the victim's boyfriend was over at the house Saturday night and the couple had been fighting recently. She had been trying to end the relationship.
The Los Angeles County Sheriff's Department had no information about any potential suspects or other details.
"I know that the deputies who arrived on scene first have talked with many people in the area and our investigators will be doing the same, but these kind of investigations - homicide investigations - are very lengthy and very detailed," said sheriff's Lt. Dave Dolson.
Neighbors said they lived at the home for about a year and kept to themselves. Some of the children are toddlers.
"This is something they'll never get over, they'll just learn how to live with the pain and carry on their life as best as they can to carry on their lineage for their mom and be there for the younger children," said neighbor Tamika Knight.
Family members say she had four children of her own and two that she adopted from her sister.
Sheriff's officials said the children are under the care of authorities.
The woman's family says she was a caring person and they knew something was wrong when she wasn't at church Sunday morning.
Anyone with information is urged to call the Los Angeles County Sheriff's Homicide Bureau at (323) 890-5500.
City News Service contributed to this report.