Evie Mills, who suffered a fractured skull and wounds to her legs, chest, hip and wrist in the bombing, was among the young fans surprised by the singer at the Royal Manchester Children's Hospital.
The international superstar was "lovely, adorable and humble" as she brought sunflowers and teddy bears as gifts, hugged victims and posed for selfies on Friday night ahead of Sunday's benefit concert in the city.
Mum Karen Mills said the visit was "unbelievable" and provided 30 minutes of "pure happiness" for her daughter and the youngsters who were caught up in the May 22 attack.
Evie, who has been allowed home to Harrogate for an overnight visit, told the Press Association: "It was so good. She just kept hugging us."
Mrs Mills, 42, added: "I think Evie is just buzzing from the visit last night and to go home and see her friends as well."
Describing Grande's visit, Mrs Mills said: "She came in and she was just lovely, adorable and humble - and all over the girls.
"There was only Jaden and Evie left in the room and she said: 'Tell me what to do, I can't do enough for them, I needed to get back.'
"She was just lovely, really lovely."
Mrs Mills said the attack had "thrown a group of people in hospital together that probably never would have met".
"I think it's going to be a really long recovery process for them," she said.
"We've had such down days in the hospital, and I think these girls have got a lot to go through still once the wounds have healed.
"So just seeing them smile and having 20 minutes, half an hour of pure happiness is unbelievable."
Evie was with friend Millie in the foyer of the Manchester Arena when the bomb exploded.
The pair, who were due to be picked up by Millie's dad, ran back through the main concourse and hid in a doorway as they fled the carnage.
Evie was "unbelievably distressed" when she spoke to her parents on the phone, but was comforted by two teenagers as she awaited treatment until they arrived.
"Millie and Evie were going to be separated - because of their injuries - to different hospitals," Mrs Mills said.
"These teenagers, we spoke to them on the phone and they said they'd stay with her. And they've kept in touch, they've been to see her in the hospital."
Evie is hoping to attend Sunday's One Love Manchester Concert but Mrs Mills said the family has so far been unable to secure tickets - along with many other girls on the ward.
"Evie can go, as long as we can get access to a wheelchair and crutches. The problem is we can't get through to Ticketmaster," Mrs Mills said.
"It's meant to be for the victims - and the girls have got it in their head that they want to go."
She added: "The hospital have been brilliant. They've really tried but they need to concentrate on nursing and caring."
Musicians including Justin Bieber, Katy Perry, Coldplay, Take That and Miley Cyrus will join Grande for the event, which is raising funds for victims and their families.