The former wife of Sir Paul McCartney grew up in a troubled household, with her mother Beatrice abandoning her three children after allegedly suffering years of domestic abuse at the hand's of Mills' father John.
Mills relished the chance to get close to her mother again in her late teens, and stayed at the matriarch's bedside when she entered hospital for a routine operation on her leg.
But the reunion was destined to be short-lived as the charity campaigner lost out on the chance to say goodbye to her mum as a blood clot claimed her life - because she got into a brawl while buying new pyjamas for her mother's hospital stay.
She tells U.K. show Shrink Rap, "My mother lost her leg at the same age and in the same place (as me). Years and years later, when she was 47, she had bad blood circulation in it and they were going to do a very small procedure of vascular surgery. She was in the Middlesex hospital in London, and she had asked me to go and get some red pyjamas because her wound was leaking so much in her white ones that she was fed up of changing them.
"So I went to (U.K. retailer) Topshop on Oxford Street, and walked up these escalators and there were these two ladies in front of me - young teenage hard (tough) girls. I said, 'Excuse me, if I could just get by,' and they just moved out of the way and tutted. And I just went, 'Sorry?' and started to walk up. The next thing I felt was this girl pull my hair and down the escalator and I remember tumbling on the floor and this fight, but all I remember was I have to get back to my mother. And when I got back she had died, and it had literally been three minutes.
"So If I hadn't got into this fight with this girl, I might have got to say goodbye. And for the first time in my life, all my anger came out, and I just kicked the furniture around the room."
Mills lost her left leg below the knee aged 25 after a police motorbike knocked her down while responding to an emergency in 2003.