British IS recruiter Sally-Anne Jones was reportedly killed in a US drone strike in Syria in June.
Jones, from Chatham in Kent, joined so-called Islamic State after converting to Islam and travelling 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, 48, who had no previous military training, 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.
News of Jones's death was not made public earlier this year amid fears that her 12-year-old son, Jojo, may also have been killed, according to The Sun.
Major General Chip Chapman, the former Ministry of Defence head of counter terror, said Jones would have been a "significant" target as a result of her alliance with Hussain and her role in recruiting IS fighters.
Responding to reports her son was killed in the strike, he added: "It is a difficult one because under the UN Charters he is under the age of what we would classify as a soldier."
A Foreign Office spokeswoman said: "We do not comment on matters of national security."