Hirschfeld is Ngāti Porou, and lost her mother when she was ten.
Hirschfeld started her career after going to the ATI journalism school, at what is now Auckland University of Technology, in Auckland. She later took a job as a sub-editor with TVNZ, eventually becoming a current affairs director/producer for Frontline and Assignment. She was also briefly a presenter-reporter on Fair Go and co-presented Crimewatch with Ian Johnstone for several years. In 1998 she left TVNZ to become a newsreader on TV3's 6.00pm bulletin with John Campbell. Together the pair also created and produced Home Truths, a late night interview show, and A Queen's Tour, a travel series retracing Queen Elizabeth II's royal tour of New Zealand in 1952. In 2005 Hirschfeld and Campbell stepped down and were succeeded by Hilary Barry and Mike McRoberts. Hirschfeld moved with John Campbell to his then-new 7.00pm weekday current-events show Campbell Live as the producer, taking the role as presenter on Fridays. Hirschfeld left TV3 in August 2009 to become head of programming at Māori Television.