And how when she found out about it via Facebook, her mother decided to make a video in retaliation, because nothing was going to stop her Josie.
"She may not get to dress up and dance," Josie's mother posted on the video, which is also a celebration of the teenager's life.
"But ... I will continue to dance with her, even if no-one else does"
Josie Webster is 16 years old and has Down syndrome.
But being a special needs kid has never stopped her from doing just about anything.
She plays the drums, dances and goes on adventure holidays.
She rode the Shotover River in New Zealand as a nine-year-old.
At the age of ten, she journeyed to Uluru in Central Australia.
She's been jungle surfing in the Daintree in Queensland, and crawled through the underground war tunnels of Vietnam.
She swims waterfalls and is a regular dancer at music festivals.
But last Thursday, Engadine High in southern Sydney held its Year Ten school formal and didn't invite Josie.
The school dance was a lavish affair at Doltone House, an "elegant ... exclusive, prestigious" function centre, according to its website, which is just 20 minutes from Josie's school.
Every Year Ten pupil, except four special needs students including Josie, were invited.
The girls dolled themselves up in party dresses, the boys donned suits and ties and the excited teenagers jumped into hired Hummers and headed off for their big night.
Afterwards, they posted photographs of themselves beaming in their party clothes on Facebook.
Until then, neither Josie nor her mother, Julie Webster, knew a Year Ten school formal had even been planned.
To top it off, proceeds from ticket sales for the dance were going to fund the Engadine High School special needs unit where Josie is among a number of students with "mild" or "moderate" learning difficulties.
Another special needs student bought a dress in anticipation of a pre-Christmas party, only to find out on Facebook the formal had already taken place.
"She was devastated," Julie Webster claims.
School principal, Joanne Jarvis, refused to comment, although she has sent an email to Mrs Webster saying the school had no involvement in the party.
A NSW Department of Education spokesman said the formal was a "private party" which the school had "nothing to do with".
He said if teachers were there, they had attended in a "private capacity".
Julie Webster said the evening was promoted as a fundraiser for the school, other mothers had told her the directive for the event had come from the school and it was a "slap in the face" for the students in the special needs unit.
She said it was "very disappointing" for Josie, and she had made a video about Josie's life to show her daughter's enthusiasm, positive attitude and how a disability had not held her back.
On the video, which she made herself last Friday with photographs and footage of her daughter, Mrs Webster tells the story of Josie and the school dance.
"Josie has done many great things in her life, but she and the other children of the support unit were not worthy enough to receive an invitation," Mrs Webster wrote.
"On the day of Nelson Mandela's passing, one of the greatest activists of all time against prejudice and hatred, bigotry is alive and well ... society needs to wake up!
"This is a mother's acknowledgment of my daughter's achievements.
"She may not get to dress up and dance.
"But her life is more of a dance than most.
"I will continue to dance with her, even if no-one else does.
"I am blessed xxxx."
After less than 48 hours on YouTube, the video has had more than 5600 hits, and the Webster family have had dozens of phone calls and messages from friends.
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Story Written by Candace Sutton