A Houston woman got an abortion for her 12-year-old mentally disabled daughter in an effort to hide evidence that her son sexually assaulted the girl, authorities said.

The woman made her initial court appearance Monday on a charge of tampering with evidence. Prosecutors allege in court documents that she took her daughter to a Cleveland clinic, where she had an abortion on Oct. 22.

Her 19-year-old son was indicted earlier this year on three counts of aggravated sexual assault of a child under 14 years old.

The names of the accused are being withheld to protect the girl's identity. The Associated Press doesn't identify sexual assault victims.

During an interview with investigators in December, the girl, who has moderate mental retardation, said her brother had sex with her in March 2010 and on several other occasions.

"She said she got pregnant because he had sex with her and said her mom took her to Ohio to have an operation so it wouldn't hurt when the baby came out. (The girl) said she told her father ... that her brother ... was the father of the baby," according to a probable cause affidavit.

Authorities say the mother knew of the investigation in the case and she "attempted to conceal evidence, the fetus/biological evidence, by taking (her daughter) to have an abortion in Ohio so the evidence would not be available for the investigation," according to the affidavit. Investigators say they recovered the fetus. The girl was about 22 weeks pregnant at the time.

The 50-year-old mother had tried getting the abortion a week earlier, but her daughter was too hysterical at the time, according to court documents.

Court records did not show an attorney for the woman, who made her initial court appearance on Monday. She did not immediately return a telephone message left Tuesday at her home.

Her son's attorney, Christian Capitaine, said that the mother, as a concerned parent, had every right to seek an abortion for her daughter, whom the woman might have believed would not be capable of taking care of an infant.

"I do expect the evidence will show she did not do that in order to prevent her son's prosecution or in order to somehow tamper with evidence," Capitaine said.

Capitaine said that at the time of the abortion, the mother was unaware an investigation was going on that was focusing on her son and that the son wasn't charged in the case until April.

"What you have is a case where folks are jumping to conclusions," he said.

Capitaine said the son denies sexually assaulting his sister. His case has not been set for trial.

The girl, now 13, and her 12-year-old sister were taken into custody in November by child welfare officials. The girls' family relinquished their parental rights earlier this month and the girls remain in foster care, said Gwen Carter, a spokeswoman for the Texas Department of Family and Protective Services.

"The girls are doing as well as can be expected. Our plan is to look for an appropriate adoptive home for them," Carter said.