Texas police are investigating whether a possibly depressed 25-year-old mother hanged her four young daughters — killing three of them — before hanging herself.

The bodies of Gilberta Estrada and her children were found hanging in a closet from pieces of clothing and sashes in their mobile home Tuesday morning. Her fourth child, 8-month-old Evelyn Frayre, was found hanging but alive and was in good condition at Cook Children's Medical Center in Fort Worth, Parker County Sheriff Larry Fowler told FOX News.

The dead woman's sister, who also lived in the Oak Hills mobile home park, about 25 miles west of Fort Worth, found the bodies, Fowler said. Alejandra Estrada came over to the house to find out why her sister hadn't left for work that day and forced her way into the locked home.

"Upon entering the residence, she had discovered what went on over here," Fowler said. "She heard some noises, she found the 8-month-old, it was still alive, she took it down."

She called 911 and said through sobs that the infant was dying. She and her daughter called back two more times to ask the ambulance to hurry, according to a tape of the calls.

Authorities did not immediately identify the other children, but Fowler said they were apparently ages 5, 3 and 2.

Filly Echeverria, who said she was the children's godmother, identified the dead as Maria Teresa Estrada, Janet Frayre and Magaly Frayre.

"It's horrendous; that's all I can say," he said. "It's just something you don't want to see."

Fowler told FOX News there was no sign of struggle but officials still won't talk about any leads or motive they have for the killings.

The hangings appeared to be murder-suicide because the trailer's doors were locked from the inside and a relative said the woman had been depressed, Fowler said.

He said Estrada had won a temporary restraining order in August 2006 against Gregorio Frayre Rodriguez, believed to be the father of the infant and some of the other children, after an attack on Estrada.

The couple had stopped living together in February, Fowler said. Tuesday was the first emergency police call to Estrada's trailer, and Fowler said there was no evidence that Rodriguez abused the girls.

Attempts to reach Rodriguez were not immediately successful.

Child Protective Services will decide who takes custody of the baby, Fowler said.

The sheriff's office is leading the investigation and is being aided by county officials, Texas Rangers, and the local medical examiner.

"It will be some time later until we find out exactly what happened," Fowler said.

Neighbors in the rural community of 1,600 were stunned. Less than five years earlier, another Hudson Oaks family was torn apart when Dee Etta Perez, 39, shot her three children, ages 4, 9 and 10, before killing herself.

The young mother and her girls were last seen alive Monday evening, he said. She was believed to be separated from her husband, who Fowler said has been notified of the deaths.

"I just got a big kick out of watching the kids play over there on her porch, and today it's sad, very sad," said neighbor Joyce Harris.

Texas has seen a disturbing number of child killings by mothers in recent years.

Andrea Yates drowned her five children in the family's Houston bathtub in 2001. In 2003, Deanna Laney beat her two young sons to death with stones in East Texas, and Lisa Ann Diaz drowned her daughters in a Plano bathtub. Dena Schlosser fatally severed her 10-month-old daughter's arms with a kitchen knife in 2004.

All four of those women were found innocent by reason of insanity. Yates initially was convicted of capital murder, but it was overturned on appeal.

The Associated Press contributed to this report.