The Home Office called the claim “speculative” and alleged that Begum had never referred to trafficking in media interviews from the Syrian camp where she is detained.
Friday’s hearing was the latest stage of a long-running legal battle over the government’s removal of Begum’s British citizenship.
In February, the Supreme Court ruled that the former Isis member could not return to the UK to fight her case, which sits with the Special Immigration Appeals Commission (SIAC).
Her lawyers told the court the Home Office had a legal duty to investigate whether Begum was a victim of trafficking when her citizenship was revoked on security grounds in 2019.
Samantha Knights QC said counter-terror police “had suspicions of coercion and control” at the time Begum left the UK, which she argued “gives rise to the need to investigate the issue of trafficking”.
In written submissions, Begum's legal team said the Home Office failed to consider whether she was “a child trafficked to, and remaining in, Syria for the purposes of sexual exploitation and forced marriage”.
Begum also wants to challenge the removal of her British citizenship on the grounds that it made her “de-facto stateless” and that the decision was procedurally unfair.
Begum left the UK for Syria aged 15, with two other schoolgirls from Bethnal Green in east London.
She was nine months pregnant when a journalist found her in the al-Hawl camp in northern Syria in early 2019, and her baby son later died.
Ms Knights told the court that Begum is currently held in the al-Roj camp in northern Syria, which is run by the Syrian Democrat Forces (SDF), where “at least two” British nationals are said to have died amid “dire” conditions.
The barrister described the camp as a “fundamentally unsafe environment”, adding: “Physical violence is common and psychological trauma is endemic.”
The SDF, which also runs other camps and prisons for people captured from Isis territories, has repeatedly asked the UK and other countries to repatriate their nationals.
But the British government has been depriving surviving Isis members their UK citizenship in a bid to stop them returning.
Ms Knights said Begum was “living in a situation of serious and present danger” and asked SIAC to consider her proposed new grounds of appeal in November.
David Blundell QC, representing the Home Office, said Begum should not be permitted to change her grounds of appeal after two years of legal argument.
He argued that while Begum left the UK aged 15, she “remained in Isis territory in Syria for a considerable period of time as an adult” and only left when the terrorist group’s “caliphate” was defeated.
“It was at that stage, not when she was a child, that the deprivation decision was taken,” he added.
In written submissions, Mr Blundell added: “It is significant that the allegation is not that Begum was trafficked, but rather that she 'may have been' trafficked.
“Begum herself has never stated that she has been trafficked, despite having given numerous media interviews and provided instructions to her solicitors on a number of matters.
“The absence of a claim that she has in fact been trafficked means this ground proceeds on an uncertain factual basis; it is entirely speculative.”
The Home Office also argues that Begum's case should be put on hold until a separate case before SIAC, which is due to be heard next March, has concluded.
At Friday's hearing, the commission also considered the cases of three women who have all had their British citizenship revoked on the grounds of national security.
The three women, known only as C8, C10 and D4, are currently held in “appalling conditions” at the same al-Roj camp as Begum.
Their barrister, Julianne Kerr Morrison, said C8 has two “very young” children with her in the camp, while C10 has “four young children with her, two of those have ongoing health issues”.
Ms Morrison added that D4 was “seriously unwell” and has also been suffering from coronavirus.
Mr Justice Jay, who is presiding over the case, said he would aim to give his ruling in the last week of June.
Of around 900 people who left Britain to engage in the conflict in Syria and Iraq since 2014, around a fifth had been killed and 40 per cent have returned.
Additional reporting by PA