It happened slowly at first: "She started struggling in school a little bit, which was fine and normal enough. But then there was one day that we were out on our bikes… and she literally fell off her bike in front of me onto the road." And: "Not long after that, we were out for a walk – we live on top of a hill – and we were halfway down and she sat down and she said, I can't, I can't get up." Then, things started to accelerate: "I remember very quickly after this that her right eye turned almost inwards… that frightened everybody." And finally, everything happened at once: "Pretty soon after that, she was diagnosed with this acquired brain injury and her life was threatened, she was very, very ill."

Tammy Darcy spoke to Ryan this morning about how her life and her family's lives changed when she was 14: "First of all, my parents separated. It's a common thing, but it's a horrible thing… And just after that, Shona was diagnosed with an acquired brain injury and she got very sick very quickly." Shona, 18 months older than Tammy, had brain surgery in the UK and rehabilitation in Dublin. But things never went back to the way they were: "When she went for the operation, she never came back… so there was never a time after that when she was the sister that you would imagine your sister would be."

 "They saved her life, but she's very badly damaged."

Shona's injury has meant that she is profoundly physically disabled and has severe mental difficulties. Tammy told Ryan that her physical condition was evident straight away, but the mental impairment took longer to develop. And while Shona became the focus, the teenage Tammy – who had previously been a part of a very strict household – was no longer kept on any sort of leash at all.

"My mother basically gave up her whole life to care for Shona as much as she could."

Now, more than 20 years later, Shona is in full-time care. The family finally realised after a bout of pneumonia, that they could no longer care for her, given her severe condition.

"The life that she has at the moment, you wouldn't want for anybody. She's very physically disabled, she needs 24-hour nursing care. And mentally, she's very, very troubled."

So Shona now receives her care in a facility in Bray: "The only place in Ireland that can fulfil her needs is a place in Bray… and she's getting the best of care there." Tammy goes to see her, but it's almost always difficult. Shona's condition means she can be very aggressive, even violent and she seems to direct much of her anger at her sister.

"Sometimes if you catch her at the right time and you make a joke or try and say something witty, she'll break down and she'll just cackle and laugh and then you have her back again for a minute. But sometimes you don't and you just have to get back in the car and drive back home again."

Given her own experience, and the fact that no one ever sat the young Tammy down to ask her how she felt while her life was being turned upside down, and the fact that she often felt hugely guilty about her sister's appalling situation, Tammy set up a charity – The Shona Project – which aims to help young women through the various challenges associated with growing up in the world today.

The Shona project can be found at shona.ie.

And you can hear the full discussion with Tammy, as well as the rest of The Ryan Tubridy Show here.