The mother of a teenage girl who was struck by a car and killed after she fled a stationary police vehicle on a motorway has paid tribute to “the most kindest, caring, loving, loyal girl ever”.

Tamzin Hall, 17, had been arrested and was being transported to custody when the police vehicle she was travelling in stopped on the M5 northbound between Taunton and Bridgwater in Somerset on 11 November.

Tamzin, a student from Wellington, Somerset, left the police vehicle while it was stationary, jumped over the barrier and was struck by a car on the southbound carriageway between junctions 24 and 25.

A hearing before a coroner on Tuesday heard the reasons the police vehicle had stopped are “yet to be established” and an inquest before a jury at a later date will be required to examine the full circumstances surrounding Tamzin’s death.

In a statement released after the hearing, Tamzin’s mother revealed her daughter had been diagnosed with autism spectrum disorder, which meant she was “unique and saw the world in such a different way”.

Describing her eldest daughter as her “best friend”, Amy Hall said: “Tamzin was the most kindest, caring, loving, loyal girl ever. She was the most honest person I’ve ever known; she was very special to me. She had a great sense of humour, and we had many laughs together.

“She was my shadow from the moment she opened her eyes in the morning until she went to sleep at night. She was such an intelligent young girl and had such interesting perceptions on things in life.”

Hall said Tamzin loved talking, family and chocolate, adding: “She was always so thoughtful and would put others before herself.”

“Tamzin was such a wonderful daughter. She was a beautiful person,’ she said. “My life will never be the same but I’m using my strength for my other children, Tamzin’s siblings.”

“I will never ever get over it, she was taken far too young.”

The coroner’s officer, Ben Batley, told the opening into Tamzin’s inquest that her injuries were not survivable, and was pronounced dead at the scene at 11.10pm. She was identified using fingerprint comparison, the hearing in Wells heard.

An initial Home Office postmortem gave Tamzin’s cause of death as head, neck and chest injuries pending further investigations.

Avon and Somerset police and the Independent Office for Police Conduct continue to investigate the death, the inquest opening heard.

The senior coroner said she would want to consider any potential mental health history as part of the inquiry and would want to explore the reasons why the teenager was being transported in the police car and how she left the vehicle.

Marsh said a jury inquest would be required as Tamzin died while in “state detention”.

The coroner adjourned the inquest to 5 November next year, when a pre-inquest review will be held.

A book of condolence was opened after Tamzin’s death in Court Fields school, Wellington, where she was a former pupil.