Lyndsey Miles was staying at the Gilbert, Ariz., house of one of her closest friends when she was shot with a handgun at around 4 a.m. Sunday, police said.
Police arrested 40-year-old Michael Craig Lance in connection with the killing. He was a roommate in the home, where a single mother and her 15-year-old daughter also lived.
Lance was booked into Maricopa County jail on suspicion of second-degree murder and possession of drug paraphernalia. He is being held on a $1 million bond.
Miles' friend called 911, but she was pronounced dead at the scene from her injuries. No one else was hurt.
Police said they don't know why Miles was shot.
They said Miles and the other girl were close and that Miles had slept over many times before.