The Sydney woman whose teenage brother shot dead police accountant Curtis Cheng reportedly became a high-level recruiter for Islamic State in Syria before she was killed in a US air strike.

Mr Cheng, left, is mourned by his wife, two children.

Former Parramatta resident Shadi Jabar, 27, helped plan attacks on the West and used the encrypted messaging application Telegram to urge fighters and women to go to Syria.

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She fled Sydney on October 1 last year, the day before her 15-year-old brother Farhad Jabar shot Mr Cheng outside Parramatta police headquarters before he was shot dead by police.

Shadi Jabar and her husband Abu Saad al-Sudani were killed in a US air strike on the Syrian city of Al Bab on April 22, according to the US government.

Using the name Umm Isa al Amrikiah, Shadi Jabar posted messages spreading Islamic State ideology and criticising men who didn’t join the fight and appeared to have risen to senior ranks in Islamic State’s propaganda wing.

Farhad Jabar was allegedly influenced by older figures. ABC

Her account contained pictures from Syria, including one of a pistol and what she said was a suicide belt along with the words “May Allah … grant me the opportunity to use it soon”.

Australian Federal Police Assistant Commissioner Neil Gaughan said about 15 Australian women are believed to be in Syria, including five who went there from Melbourne to become jihadi brides in the last nine to 12 months.

Most of the women were between 19 and 25, and Assistant Commission Gaughan warned Syria was not the glamorous destination it was portrayed as on social media.

“It’s a war zone,” he told News Corp.