According to authorities, police said they received a call around 7 p.m. on June 28. When they went to the Las Vegas home, they found the girl and her 2-year-old sister locked into a hot bedroom with no air conditioning.
Officials said the high in the neighborhood where this happened was 107 degrees.
The 2-year-old was still alive and taken by Child Protective Services, police said.
Witnesses told KLAS the mother, Kemaya Darshay Taylor, 23, was outside throwing rocks at cars and acting erratically.
Officials said the incident is still under investigation and the cause of death for the 5-year-old is still being determined.
Taylor has been arrested and charged with murder. She also faces two counts of felony child abuse, police said.