Ms Ironside, who has written agony columns for women's magazines and the Independent for many years, said she was convinced she had "done the right thing". Her mother, who previously had made two suicide attempts and was in unbearable pain, thanked her for her action, she claimed.
Ms Ironside's mother was an alcoholic who was suffering from breast cancer. Ms Ironside did not ask the doctors directly to give her mother a fatal injection - "it was not actually spoken, it was important to get the words right" - but there was a clear understanding between them about what she wanted.
"As they were preparing to give her another blood transfusion, I said to her doctors: 'How can you do this? She doesn't want to live' - and I burst into tears.
"It was quite clear what I was saying. The doctors replied: 'Ah well, maybe you have a point, maybe we can give her an injection to heal her pain." The injection was given and she died.
Ms Ironside said her mother, who died 20 years ago almost incoherent with pain, was grateful for her daughter's action. "I said: 'Don't worry Mummy, it's oblivion from now on. I've organised it'." Her mother had replied: "Thank you."
"She knew what I'd done ... I felt a great relief because she had wanted to die. There was no question about it. My father said to me 'You did exactly the right thing'."
Ms Ironside claimed she even had support for her decision within the hospital. "Earlier I had come into the hospital and a nurse came up to me. She said: 'Please, please, I'm a Catholic, but your mother is in terrible pain, she is full of cancer, she is depressed and unhappy, and there are things doctors can do - ask the doctors to do it'."
Helping to ease patients' pain is legal, but physician-assisted suicide and euthanasia is currently illegal. The British Medical Association opposes any change in the law, but earlier this year it voted to hold its first conference on the ethics of helping patients to end their lives, saying it was essential that doctors reached a consensus.
Clarity is being sought in particular for when a doctor gives increasing doses of a drug in the knowledge that it may shorten a patient's life.
Last month, the murder trial committal took place of Dr David Moor, a Newcastle GP at the centre of a mercy-killing controversy. He was investigated by police after speaking to newspapers in support of Dr Michael Irwin, a former medical director of the United Nations and the World Bank, who was reported to have ended the lives of at least 50 terminally-ill patients.
Ms Ironside is training as a bereavement counsellor with Cruse, an organisation that helps people get over the loss of a loved one. She has written books previously on bereavement, including You'll Get Over It after her father died six years ago.
She said it was important to realise there was no "right" way to grieve for a person and that bereavement affected people differently. "Some people feel nothing, some people feel relief, some people feel physically ill," she said.
"Feelings of bereavement are usually fairly chaotic. We must realise that there is no particular way of grieving."
Cruse: 0181-940 4818Reuse content