Demi memiliki saudari tiri yang [[disabeldifabel]], dan Demi pernah mengatakan bahwa ia adalah motivator terbaik dalam hidupnya.<ref name="Ghosh">{{Cite web |url=http://www.ibtimes.co.uk/miss-south-africa-demi-leigh-nel-peters-beats-colombia-jamaica-win-miss-universe-2017-1648983 |title=Miss South Africa Demi-Leigh Nel-Peters beats Colombia and Jamaica to win Miss Universe 2017 |last=Ghosh |first=Sutrishna |date=2017-11-27 |website=International Business Times UK |language=en-GB |access-date=2017-11-27}}</ref> Demi sarjana jurusan Bisnis Manajemen di North-West University,<ref name="Bustle"/><ref name="CBS AP">{{Cite web |url=https://www.cbsnews.com/news/miss-universe-2017-winner-miss-south-africa-demi-leigh-nel-peters/ |title=Miss South Africa Demi-Leigh Nel-Peters wins Miss Universe |date=2017-11-26 |website=CBS News |language=en-US |access-date=2017-11-26}}</ref> dan ia fasih berbahasa [[Bahasa Inggris|Inggris]] dan [[Bahasa Afrikaans|Afrikaans]].<ref name="Bustle">{{cite web|url=https://www.bustle.com/p/miss-south-africa-demi-leigh-nel-peters-wins-miss-universe-2017-5553502|title=Miss South Africa Demi-Leigh Nel-Peters Wins Miss Universe 2017|date=26 November 2017|publisher=Bustle|last=Denninger|first=Lindsay}}</ref>
