She has always had a vested interest in politics and wanted to experience "first hand" what it is like.
"I am passionate about bringing change to issues of this area. I'm hoping to see some of the major issues around this country improved, such as child poverty, environmental issues etc."
But her main passion is addressing youth mental health and suicide.
"I think the suicide rates in the whole country are shocking, but particularly having a mother that works at Oranga Tamariki really opens me up to the issues of mental health and how that stems from domestic violence and sexual violence."
She was one of eight students to apply for the role and had to send through a video for the interview process.
Nash wonders whether the small number is "symptomatic of what young people think of politics", but nevertheless, Sarah stood out.
"I thought she would be a fabulous representative for not only me and my office, but also the city of Napier. She's passionate, she's extroverted, she's everything you want in an MP, and she loves politics."
Her tenure as youth MP goes from March through to August. As part of the programme, the Year 12 pupil will next year attend a two-day Parliament in Wellington as a Youth MP for the electorate to debate issues that youth candidates have selected.
Before that, the 17 year old will be shadowing Nash to see what is involved in representing the electorate - including accompanying him at street corner meetings.
She has already had several meetings with him and has also spoken on a panel for health policy in November.
Where to get help:
If you are worried about your or someone else's mental health, the best place to get help is your GP or local mental health provider. However, if you or someone else is in danger or endangering others, call police immediately on 111.
• Lifeline: 0800 543 354 (available 24/7)
• Suicide Crisis Helpline: 0508 828 865 (0508 TAUTOKO) (available 24/7)
• Youth services: (06) 3555 906
• Youthline: 0800 376 633
• Kidsline: 0800 543 754 (available 24/7)
• Whatsup: 0800 942 8787 (1pm to 11pm)
• Depression helpline: 0800 111 757 (available 24/7)
• Rainbow Youth: (09) 376 4155
• CASPER Suicide Prevention
• Lifelink/Samaritans: 0800 726 666 (available 24/7)
If it is an emergency and you feel like you or someone else is at risk, call 111.