Skye Mason, who is charged with taking baby Alyssa Barker from her North Auckland home, had a childhood of drugs, broken homes and teenage pregnancy.
Her sister Calah Mason, 26, told the Herald on Sunday: "Skye has never really had a family, a father figure or a mother figure ... She's just a lost soul."
Calah said Skye, 27, had three sons aged between 3 and 11, but had custody of none. She understood two lived with their fathers and one was in foster care.
Calah said Skye would never have harmed a child.
Skye was the oldest of four girls born to Amanda Mason. Skye and Calah had different fathers and the younger sisters were born to a man who gained custody of all four when Skye and Calah were little.
"Skye was not an easy child to deal with. At one of the properties we lived in, she was basically living in the garage," said Calah.
Skye had trouble at school - Kingsway Christian School and Orewa College - but loved animals and children.
"She just didn't quite fit in right. She was not so eccentric as she is now," said Calah.
At 13 or 14, Skye moved with her mother to Australia, but about age 15, she returned to New Zealand and became involved in drugs. She had her first child when she was 16 to a man who was about 20 years older than her.By Kathryn Powley Email Kathryn