Ms Gilderdale (55) faced a life prison sentence for giving Lynn morphine and a cocktail of drugs to commit suicide after her 17-year battle with the illness ME.
The devoted mum, who was arrested while her daughter lay dead in their home, has recalled the numbness she felt as she lay on a bare bed in a freezing cold cell.
"They took me to the custody block, where I had to hand over everything I had with me. Then I was shown to a cell and two female police officers came and strip-searched me. They took my shoes, socks and tee-shirt but left me my jeans and cardigan.
"They photographed my body to look for bruises as evidence of any kind of fight. Two nurses took blood and urine samples and swabs. They even snipped bits off my nails -- everything to look for signs of a struggle."
Kay grew up in Mount Merrion, Dublin, before training as a nurse in the UK. She explained how her daughter begged her to help her die. For 17 years, Kay (67) watched Lynn struggle with an acute form of Myalgic Encephalomyelitis (ME) that had left her bed-bound.
Many in the medical profession dismissed the disease -- also known as chronic fatigue disorder -- and told Lynn "she was pretending" to be ill .
However her post-mortem revealed that her body had broken down from the illness.
On December 3, 2008, Lynn, who had been talking about suicide for two years -- and who had already attempted it once -- injected herself with 210mg of morphine. It wasn't enough, so she pleaded with her mum to hand her another dose.
"I knew instantly what had happened: she had injected the entire contents of the syringe into her bloodstream. She was crying as she signed to me, 'I can't take any more. I can't go on... I have taken all this morphine already, but it is not enough. Please, Mum, you must get me some more,' she told me," Kay recalled.
"I thought about all the things she'd put up with in 17 years of illness -- people disbelieving her, doctors sticking huge needles into her spine, her veins collapsing, contracting MRSA in hospital.
"Now, she was suffering kidney and heart problems, osteoporosis, liver dysfunction, adrenal failure and an underactive thyroid. I couldn't see how she could ever lead a normal life."
Lynn had explained to her parents on numerous occasions that she no longer wanted to live, and by December 2008 she had insisted she should not be resuscitated if she took a turn for the worse and that she no longer wanted to go to hospital.
After hours of pleading, Kay eventually accepted her daughter's decision and handed her more morphine.
Later, when her daughter seemed in pain, she diluted some of her pain medication and pushed it down her feeding tube, and attached another dose of morphine to the syringe driver in her thigh. Nearly 30 hours after she had called for her mum, Lynn stopped breathing.
Kay called her ex-husband Richard to their home in Stonegate, a village in east Sussex, to say goodbye to their daughter. He contacted the coroner and explained what had happened, that Kay had 'given' Lynn morphine. This was misunderstood and Kay was arrested.
She was then charged in April 2009 with attempting to murder her daughter. However in January 2010, a court ruled that Kay was not guilty.
During the trial, a letter Lynn had sent to her internet friends, in November 2008, was read out in court in which she stated that she hoped they could find it within their hearts to understand why she wanted to die.
Kay told the Herald that she decided to write a book about her daughter's illness so they would understand how difficult Lynn's decision had been and how much she had been through.
"I got the impression that people didn't realise what a strong personality she was and exactly what she had gone through," Kay said. When Lynn's body was examined by a pathologist, he discovered "dorsal root ganglionitis -- infected nerve roots -- and nodules of Nageotte , which are little tombs of dead cells, in her spinal cord".
"These would have caused her terrible pain and sensory nerve damage," Kay writes in her book, and they were just some of the many aspects of her condition. Kay admits that to this day she finds it difficult to trust doctors, because many did not believe her daughter was really ill.
"Once, she was rushed to the hospital and the doctor in the emergency car gave her oxygen but when the registrar saw that on her file that she had ME, he said that 'She's only hyperventilating, remove the oxygen, give her a paper bag and tell her to go home'," Kay recalled. Lynn actually had a clot on her lung and was saved thanks to her parents fighting the doctor's decision.
Kay travelled to Australia this weekend to visit her sister Marie. It was the first time she had left the house Lynn grew up in for any length of time.
"I have been to Ireland a few times to visit my family who are still there (many of her nine siblings are still based around the country) and I've also gone to see my son Steve in Belgium, but I haven't been away from here for a few weeks at a time.
"I know that emotionally it will be very hard, but I will make the best of it. I think of Lynn no matter where I am, but (the house in Stonegate) is just a place that I can feel closest to her.
"I miss her all the time, nothing will take away this deep sadness inside me but now I also remember the happy moments we shared, and before she was ill."
From One Last Goodbye by Kay Gilderdale, published this year by Ebury at €9.30.