Using the fake name Harper Hart, 29-year-old Samantha Azzopardi enrolled as a 13-year-old at the school late last year.
When the school asked for identification, Azzopardi said she was a victim of sexual assault and human trafficking and was under the US Government's Witness Protection Program, SMHreports.
NSW charities and government departments spent more than $155,000 on Azzopardi before realising her fraud.
She had previously used a similar story to fool authorities in both Ireland (where they spent AU$386,000 trying to identify her) and Canada (where they spent $A400,000 trying to identify her) and is known to have used more than 40 aliases over the years.
On Monday, NSW District Court judge Paul Conlon dismissed Azzopardi's appeal against a maximum one-year sentence, News.com.au reports.
“It is disturbing in the extreme that at 29 years of age she still tries to pass herself off as an adolescent,” Conlon said at the hearing.
A court-appointed psychiatrist reported Azzopardi has a "remarkably unstable sense of identity," and gave a tentative diagnosis of Borderline Personality Disorder.
She will be eligible for parole in November.
This article originally appeared on marie claire.