Tracey Cullum challenged the youngsters after they barged in front of her at a bus stop in Birmingham. One of the teenagers struck the 31-year-old mature student in the face with such force that it spun her around, breaking her ankle. She was treated for the leg injury and facial bruising before being released from hospital.

Last Friday she complained of tiredness and then suffered a blood clot to the heart. She died as her partner was taking her to hospital. Doctors said that the attack had triggered her death. A post mortem examination found that she had died from a coronary embolism.

Mark Holiday, 37, Ms Cullum’s partner, said: “She was so fantastic, so kind and bubbly, she put everyone she met at ease. She just drifted away from me and I didn’t even get the chance to tell her I loved her. She kept whispering to me for help while she was half-conscious, but there was nothing I could do.

“After the incident we thought this mess was all over, we were trying to get on with our lives and then she was just taken away from us. These people have taken a mother away from her son, and I have lost my rock.”

Ms Cullum and a friend were taking their children and two friends to a family dance event on July 2. As they waited for a bus, four youths charged to the front of the queue.

Ms Cullum challenged them before glancing behind her to check that her son had not been harmed. When she turned back to look at the youths, one of them punched her in the face, knocking her to the ground. As her son and friend tended to her, the teenagers leapt from the bus and fled.

Mr Holiday said: “What started out as a fun evening for Tracey, her friend, Ash and the other children turned into a nightmare. She was minding her own business at the bus stop when these lads just pushed in. She was badly shaken and Ashley was extremely upset.

“Tracey was told that it would take up to 12 weeks for her leg to heal and she would have to use a wheelchair and frame to walk. She coped fantastically with the whole incident and tried to get on with her life. It obviously upset her but she was mainly confused about why it had happened; why they had been so violent about such a small argument.”

He said that her health had deteriorated during the course of the day.

“She woke up feeling under the weather and was very tired’ but she got through the day and even managed to get to the shops,” he said. “When it was time to go to bed she struggled to get up the stairs, I helped her but she was finding it very difficult to breathe.

“When she finally reached the top she had a seizure and was drifting in and out. I didn’t know what was happening, I was losing her and there was nothing I could do. The paramedic told me that there wasn’t much chance, but I didn’t believe him, I couldn’t lose Tracey.

“I want these scumbags to be caught so that Ashley will grow up knowing that we live in a society where we don’t stand for violence like this.”

The four youths are described as black and were wearing hoods. The youth who hit Tracey is described as being aged 16 to 18 and 5ft 4in to 6ft tall.

Detective Chief Inspector Jan Thomas-West said: “We are now treating her death as suspicious. We would appeal for anyone on the bus or in the queue to come forward with any information.

“Equally we are keen to speak to the youths themselves. This is a tragic incident and we want to resolve it as soon as possible.”

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