[9] Since then, her books have often tackled difficult subjects such as grief, anger, violence, physical and emotional abuse, suicide and self-harm, racism, sexism, bullying and environmental issues.

[3] She writes predominately for young adults, although a shift in 2017 saw her publish Heloise (Penguin NZ), a historical novel based on the life of 12th century nun Heloise d'Argenteuil, famed lover of philosopher Peter Abelard.

[15] She also writes adult fiction, short stories, non-fiction, educational resources, blogs and articles.

Her work as a resource writer for the Global Education Centre dealt with topics such as "Weather Wars – The Politics of Climate Change, Parihaka and the gift of non-violent resistance", "Healing the World – Back to the Future", "Get Up!

[5] She has run many creative writing workshops,[17] is a frequent visitor to schools [18] and has appeared at numerous literary festivals, including the National Writers Forum,[7] the Auckland Writers Festival[19] and Verb Wellington.

The Crossing won the Young Adult Fiction category of the New Zealand Post Children’s Book Awards in 2010.

Heloise spent several weeks on the bestseller list[33] and was longlisted for the 2018 Ockham Book Awards.

[46] In 2019, Hager also received the Margaret Mahy Medal and Lecture Award, which acknowledges lifetime achievement and a distinguished contribution to New Zealand’s literature for young people.