A Sydney teenager who sent thousands of dollars to Islamic State fighters overseas is fighting an application for her sentence to be decided in the NSW District Court where she'd face a tougher sentence.

The 17-year-old, who can't be named for legal reasons, has so far had her matter heard in a children's court where the maximum sentence for the offence is two years.

But prosecutor Troy Anderson argued in the Parramatta Children's Court on Friday that a heftier sentence was warranted given the severity of the crime and her level of involvement over many months.

A teenager (R) who sent thousands of dollars to ISIS overseas is fighting an application for her sentence to go up to the NSW District Court where she would face 15 years jail

The 17-year-old, who can't be named for legal reasons, has so far had her matter heard in a children's court where the maximum sentence for the offence is two years

He said the girl arranged at least $17,000 in Western Union transfers over 2015 and 2016 to a man in Syria, who told her it would help the 'mujahideen' or jihad fight the kafir - the Arabic term for unbeliever.

'This is a very serious offence, and this is a serious example of it,' Mr Anderson said.

The maximum sentence in the District Court for an adult is 15 years, he said.

The teenager pleaded guilty in November 2016 to knowingly collecting funds - when she was a schoolgirl - for a terrorist organisation.