Cassandra Shepard told police she had moved from South Dakota to get Nina away from a life of abuse.
Prosecutors say it followed the woman here.
As paramedics worked to save Christina "Nina" Harms on the afternoon of March 25, Shepard told police that Harms had been acting out, that in a tantrum she had held her breath until she passed out.
But as investigators looked at the scene the bandages on Harms' hands and arms, the marks on her legs they began to look at Shepard as a suspect.
"We came to the conclusion that things just weren't adding up," Paul Nielsen, a former Unified Police detective, said Friday during a preliminary hearing in 3rd District Court.
After hearing from police and medical experts, Judge Randall Skanchy took the case under advisement. He will rule at a later date whether Shepard, 20, should stand trial for the murder of the woman for whom she had promised to care.
Deputy Chief Medical Examiner Edward Leis, who performed the autopsy on the 22-year-old Harms, testified the woman was severely dehydrated and had toxic levels of a sedative, possibly Benadryl, in her system when she died.
Harms had bruises on her body. Her hands were wrapped tightly in bandages to cover wounds. And she had a pepper seed in her right, lower eyelid, Nielsen said.
Harms had fetal alcohol syndrome, which caused her to function at a preteen level, friends and family have said.
Shepard was awarded legal guardianship of Harms after Harms' mother, a relative of Shepard, died in 2008.
Shepard is charged with first-degree felony charges of murder and aggravated abuse of a disabled adult, and second-degree felony obstructing justice.
Shepard's mother and stepfather Dale Robert Beckering, 52, and Sherrie Lynn Beckering, 50 also lived in the Kearns home. They were previously ordered to stand trial on charges of aggravated abuse of a vulnerable adult.