She told the BBC she could be “useful to society” and it would be a waste to let her “rot” in a Syrian camp.
The 22-year-old is accused of playing an active role in IS – she denies that.
Sajid Javid is standing by his decision to revoke her citizenship.
Shamima Begum was 15 when she and two other east London schoolgirls travelled to Syria to join IS.
There, she married a Dutch recruit and lived under IS rule for more than three years. In 2019, she was found, nine months pregnant, in a Syrian refugee camp. Her baby later died of pneumonia and Ms Begum said she had previously lost two other children
The then-Home Secretary Sajid Javid stripped Ms Begum of her UK citizenship on national security grounds.
Who is Shamima Begum and how do you lose your citizenship?
Shamima Begum cannot return to UK, court rules
Ms Begum has previously said the 2017 Manchester Arena bombing, in which 22 people – some of them children – were killed in a bombing claimed by IS, was similar to military strikes on IS strongholds and called the terror attack “retaliation”.
Asked by BBC reporter Josh Baker how it made her feel to think back to being part of a group that committed genocide and murder around the world, she said: “It makes me sick to my stomach really. It makes me hate myself.”
In the interview for BBC Sounds and BBC 5 live, Ms Begum also said she only now felt comfortable talking about her true feelings.
Our reporter asked whether she had changed her opinion on IS because it had not created a caliphate.
“I have had these opinions for a very long time but only now I feel comfortable to express my real opinion,” she replied.
She said if allowed back into the UK, she could advise on the tactics used by IS to persuade people to go to Syria and could share ways to speak to people who are at risk of being radicalised.
She said she felt “an obligation” to do so, adding that she did not want any other young girls to destroy their lives like she had