"I flew down to Wellington Hospital with him and I was terrified. He was so bad."
Manutahi was moved out of intensive care because there was nothing else they could do, she said.
"I mean, he can't talk or anything and he has had a tracheotomy now to help with his breathing. And he's being fed through a tube in his nose."
Talisha said she kept hoping the police would call with news. "The fact that there is still an investigation going on is good, but I wish they could find out who did it. It frightens me, it really does."
Her father, Leo Kahui, and little sister were staying at Ronald McDonald House, in Wellington, which was good for them.
"We can't leave Manutahi ... he knows we are here, he really does."
However, the stabbing into his cheekbone had been so violent it pushed a bone fragment into his brain, and operating was too dangerous, medical staff said.
"It's really hard, because we don't know whether his brain will ever work properly again. It makes me feel so sad for my little brother.
"He didn't deserve this. But the tracheotomy is helping his breathing and swallowing now. Of course, he can't talk or anything. Maybe he never will - I don't know."
Talisha said she was at his bedside all day, every day.
"He is very important to me ... he is very important to all of us."
Manutahi had come to Wanganui two months ago when his dad, Mr Kahui, was forced to leave his rented house in Auckland.
Some of the family were gang members but not Manutahi, Mr Kahui has said.
Mr Kahui is a Black Power member, and two of his other sons are Tribesmen members.
"He [Manutahi] is a quiet and special boy who doesn't belong to any gang. He's a big 16-year-old but he's just a big kid, really - a big gentle, kind kid."
Mr Kahui said the case rested entirely with the police.
Detective Sergeant John Gleeson said inquiries continued, and police would like to hear from anyone with information.
Police are looking for a male Maori, 1.83m (6ft) tall, with a No1 haircut. He is believed to have a beige pitbull with him.