The star recounted the experience on her social media account in an attempt to spread the word about cyber-bullying and how it impacted her young sister's life.
"This is my sister Angie, she's 13 years old. She's bright, funny, kind and caring," wrote Nation alongside a black-and-white snap her loved one.
"She also has high functioning Aspergers, anxiety and depression. She has been severely bullied for almost 3 years and the internal torment that she goes through on a day to day basis is crippling. Often, her anxiety is paralysing," she continued.
"Angie had spent the school holidays with our grandparents on their farm. It's a loving, healing place and there, she felt safe. She came home two days ago and having barely been on social media for the last 5 weeks she thought she would connect with friends online," she said before revealing her sister had contemplated taking her own life.
"My heart was in pieces when I learnt what followed," she added.
Nation noted that a girl of the same age as Angie sent her a horrible message, which read: "You know what would be better for [boy's name] and I, if you went and killed yourself. RIP."
"2 hours later, Angie had locked herself in my mum's room, threatening self-harm and phoned Lifeline," Nation continued.
"She pleaded with lifeline to help make it stop, expressing that she simply didn't want to be here anymore and she wanted to be with her dad (he passed away 4 years ago). "I want to kill myself, I'm going to kill myself, please help'', she wrote.