British IS recruiter Sally-Anne Jones was reportedly killed in a US drone strike in Syria in June.
Jones, 48, who had no previous military training, joined so-called Islamic State after she converted to Islam and travelled to Syria in 2013.
The BBC's security correspondent Frank Gardner said she had been a useful propaganda agent for IS on social media and her death would be "significant".
Her death was first reported by The Sun.
Jones, from Chatham in Kent, had been used to recruit Western girls to the group and posted threatening messages to Christians in the UK.
She used her Twitter account to provide practical advice on how to travel to Syria.
Previously a punk musician, Jones married the jihadist computer hacker Junaid Husain, who was killed in a drone strike in 2015.
Hussain was described as a key IS operative before he was killed by a US drone strike.