The woman, identified by family members as Cecelia Sanders, was found in a bedroom and had been stabbed several times, the Houston Chronicle reported.
Her 3-year-old daughter was found locked in a closet and her 8-month-old daughter was in the room with her, family members said, adding that neither child was injured.
Police said the last person to be seen with the woman was her boyfriend, Ronald Green. Neighbors saw the couple enter Sanders' apartment around noon Sunday.
Police said investigators do not yet have a motive or suspects in the stabbing.
"This is bad," said Tiffany Williams, the victim's sister-in-law. "This is something you don't want to believe. I feel like I'm dreaming."