Dublin District Court heard she had never been in trouble before and committed the crime in a "moment of madness".
McAllister, with an address at Leixlip Park, Leixlip, Co Kildare, was charged with the offence at The Lost Society, South William Street, on February 22, 2012.
The court heard she previously pleaded guilty and the case had been adjourned for a report.
This stated McAllister was at a low risk of re-offending and had no previous convictions.
The court heard gardai approached her at the premises and found her in possession of a "large amount" of ecstasy tablets, with a street value of in excess of €800.
"She has openly admitted she involved herself in this criminal behaviour to make money," Judge Michael Walsh said.
She was attending a fashion design course and her family had been considering emigrating to Canada, defence Sorcha Whelan said.
She asked Judge Walsh to consider leaving McAllister without a conviction for what was a "once off, wholly out of character event. It was one moment of madness."
Judge Walsh said that McAllister did not present as someone who was "entrenched in criminal behaviour and a criminal attitude".
She had now distanced herself from a "negative peer group" who had been involved in alcohol and drug misuse and was progressing in her studies.
"Notwithstanding this, possession of drugs for sale or supply is a very serious matter, the court is only too aware of the problems dealing in drugs inflicts on people and on society in general," the judge said.
He gave her four months to pay the fine, with five days imprisonment in default. He put her on a probation bond for a year and she must abstain from alcohol and drug abuse.