But she said things changed when she wore it on school photo day, sparking concern among Year 12 co-ordinators.
She was quickly asked to take the T-shirt off.
"They said it was because certain parents would complain," Stephanie said.
Her mother, Susan, said she had had the controversial T-shirt printed for her daughter when she was about 15.
Susan said her daughter was brave to wear the T-shirt in public and particularly at school.
"I'm proud of her," she said. "I love her and I don't care what she is."
Stephanie said she was disappointed by the school's request for her to remove the T-shirt, but understood the concerns.
She said she would wear the T-shirt to school again once the issue had calmed down.
The incident triggered a protest by other Year 12 students, who
turned up at school wearing T-shirts with similar slogans. They
included "Nobody knows I am bulimic", "Nobody knows I'm pregnant" and
"Nobody knows I'm on steroids". The students said they found the
request to Stephanie discriminatory and an attack on free speech.
Stephanie said she was shocked by the amount of support she had received. "It's pretty cool I guess," she said.
The school declined to comment this week.