She returned to her Wellington home in April, but a month later was admitted to hospital where she died from her injuries.
Before Teegan and her sibling were taken home by their parents, the hospital had warned them of the dangers of shaking a baby.
But Teegan was a diffcult baby. She cried a lot, the court heard.
Wichman had tried to give Teegan a bottle but she was still crying, the Court heard.
The 17-year-old father then shook Teegan.
Although her head didn't contact anything, she was still very fragile.
Justice Simon France acknowledged they were loving parents but struggled to bring up their twins.
"They were only teenagers, mother was only 16, trying to bring up twins who were 15 weeks premature. It must have been really hard."
Teegan's grandfather and father of Tairoa, Lance Tairoa said in his victim impact statement that he spent a lot of time with the twins.
One evening he was told Teegan stopped breathing.
"When I heard she was having seizures I knew it was something different."
Teegan was transferred to Auckland's Starship Hospital.
"I was in shock but I had to be strong for her," Lance Tairoa said.
He remembered Teegan opening her eyes as he sat at her bedside.
"Nurses gathered around her. [They] were praising her saying 'We know what colour her eyes are'."
When Teegan died in September 2009, Tairoa was sad, angry, in disbelief and beside himself.
Although others had told him this was a cold case, he never gave up.
"I promise you justice will be done."
Lance Tairoa then turned around in court and said to his family: "We must learn to love one another and support each other.
"What has happened has caused a lot of fighting and it's time to change.
"Now we can focus on the good memories and good times while Teegan was with us," he said.
Wichman's lawyer Paul Paino said Wichman was "ill-equipped" to take care of his premature children.
His risk of re-offending was low, he said.
Justice France said he didn't condone the behaviour, but there were consequences to
Wichman's actions.
The couple lost custody of the surviving twin and also their other child.
When Wichman left the dock, family members watching on, yelled "love you son".
