It's hard to find a bigger Justin Bieber fan than Hailey Roser.

The 4-year-old Wisconsin girl has two life-size cardboard cutouts of the Biebs in her hospital room, where she fights a daily battle against an aggressive form of brain cancer.

She has endured two brain surgeries -- but doctors can't remove all of her brain tumor. Facing months of radiation and chemotherapy, Hailey wanted nothing more than a visit from the pop superstar.

After a social media blitz, including the viral Twitter hashtag #justinvisithailey, a radio station helped score meet-and-greet tickets to Bieber's concert Sunday in Milwaukee.

But then a mass shooting at a suburban salon Sunday forced the hospital to go on lockdown -- meaning no one could enter or leave.

This is the story of a long cherished visit that almost didn't happen.

A simple message

The quest began in late September when a timid-sounding Hailey, with a lisp typical of many 4-year-olds, made a personal plea to Bieber in a YouTube video: "Justin Bieber, I would really like you to come and see me. I love you."

As the date of the show neared, her father, Eric, followed up with a plea of his own.

"If there's any possible way that you could meet her -- see her, come to the hospital, say hi, anything -- just for 10 minutes, it would absolutely -- I just know it would put the biggest smile on her face in a time where our family doesn't have a lot to smile about," he said.

The family's plea soon spread through the community and across social media, with tweets and retweets from well-wishers who wanted nothing more than for her wish to come true.

"EVERYBODY WHO SUPPORTS HAILEY RETWEET THIS! @justinbieber NEEDS TO SEE THIS!" tweeted Lexi Carl as she linked to a story about the girl that appeared in a local newspaper.

The sea of supporters posted videos of their own. Students and staff at Holmen High School set theirs to Bieber's song "Never Say Never." Hailey's family later credited that video for playing a huge role in getting media attention.

After a blitz of local media coverage, Hailey got the surprise of her life -- meet-and-greet tickets to Bieber's concert Sunday at the BMO Harris Bradley Center in Milwaukee.

"Can't believe it guys! @justinbieber is gonna do it! Without you guys this wouldn't have happend, thank you," tweeted a supporter, Ally Kraczek.

A roadblock

But then the unexpected occurred.

A man walked into a suburban Milwaukee salon and opened fire, striking seven people. Three of them died. The shooter then killed himself.

But in the chaos of the situation, the Children's Hospital of Wisconsin went into lockdown.

"This means nobody is allowed to come or go. What are the chances????!!" the Facebook account Healing Hailey posted.