German authorities are investigating whether a suspected Islamic State fighter seized by Iraqi forces in the war-torn city of Mosul is a 16-year-old German schoolgirl who disappeared from her parents’ home in Saxony a year ago after apparently being groomed by jihadist groups online.

The parents of Linda Wenzel have been searching in vain for their daughter since she vanished from her home in the village of Pulsnitz on 1 July last year after converting to Islam in secret.

Video footage which appeared over the weekend seems to match images of Linda. Pictures show an exhausted, dust-covered girl who was arrested by Iraqi forces as part of a group of 20 female Isis supporters from Russia, Turkey, Canada, Libya and Syria who had barricaded themselves with guns and explosives in a tunnel underneath the ruins of Mosul’s Old City.

An Iraqi commander in Mosul confirmed to the Guardian that all the arrested women had since been transferred to Baghdad.

On Tuesday, an unofficial Iraqi special forces Facebook page posted a photograph of the arrested girl, along with the caption: “It transpires that she was a German Inghimasi [suicide bomber] who worked for the police bureaus of Daesh and not a Yazidi girl … she was a teenager from Germany who travelled from Germany to Turkey and then to Syria and Iraq.”

The state prosecutor of Saxony said on Tuesday that he was urgently investigating the new evidence. “Communications with Iraq are proving difficult, but we are doing everything necessary to establish whether the girl arrested is Linda W,” a spokesperson, Lorenz Haase, told the Guardian.

Linda used to share a house with her mother and stepfather in Pulsnitz, a town of about 7,500 inhabitants between Dresden and the Polish border. Having moved to Pulsnitz following the divorce of her parents, she had soon established herself at the local Ernst-Rietschel comprehensive school as a talented student with a particular interest in maths, chemistry and physics.

But about half a year before her disappearance, classmates noticed a change in Linda’s behaviour, with the teenager swapping rap for Arab music and asking the headmaster if she could wear a headscarf at school.

In spring 2016 Linda told her parents of her growing interest in Islam, but hid the fact that she had converted to the religion. During Ramadan, she told the family she was on a diet. “We didn’t think anything of it, and even bought her a copy of the Qur’an,” her mother, Katharina, told German media.

On 1 July last year, Linda texted her mother “I’ll be back at 4 o’clock on Sunday” after having agreed to spend the weekend sleeping over at her friend’s house. But when the Wenzels called Linda’s friend on Sunday afternoon, she knew nothing of the teenager’s whereabouts.

Hidden under the mattress in Linda’s room, police later found receipts for two plane tickets, from Dresden to Frankfurt and from Frankfurt to Istanbul, which she had purchased with a faked bank authorisation and her mother’s passport.

According to sources cited by the newspaper Bild, Linda is likely to have travelled from Istanbul to the Bab al-Hawa crossing on the Syrian border, in the rebel-held Idlib province. In mid-August, she was reportedly picked up at the border crossing by members of Jund al-Aqsa (JAA), an approximately 1,000-strong jihadist group with links to Isis, who are believed to have smuggled her into Mosul, which had been held by Isis since June 2014.

At Linda’s home in Saxony investigators also discovered a prayer rug, a tablet with hundreds of photographs and the login for a Facebook account which Linda had used exclusively for keeping in touch with profiles in Arabic and sharing content such as: “Pray, the end is nigh.”

Authorities estimate that up to 930 people have made their way from Germany to Syria since the start of the war in the region. Linda is one of three who are believed to have joined jihadist groups from Saxony, a state where an estimated 0.1% of the population is Muslim.

If the arrested teenager is confirmed as Linda, she would have defied the odds to survive in a city that has been at the heart of a major military operation since last November.

One soldier described dramatic scenes at the arrest of a female sniper last Thursday: “She fought to the last bullet and she was arrested when she ran out of ammunition. She was a sniper and she was from south Russia. She had a wound on top of her head and her face has turned blue as she was beaten by the soldiers. She was taken to a field clinic to treat her and then they attached a drip to her arm to build up strength in her body. She looked very weak.”