After the 2008 recession left her redundant from her job as a learning and development executive at the Irish law firm A&L Goodbody, she decided to pursue her passion of writing.
[6] Gaynor self-published her debut fiction novel The Girl Who Came Home, based on the true story of 14 Irish emigrants on the Titanic, on Kindle in 2012.
Shortlisted for a Historical Writers' Association Gold Crown Award,[13][14] the story of Grace Darling had fascinated Gaynor from a young age.
[15] Her 2020 book, set at a boarding school in 1941 China, was published under the name The Bird in the Bamboo Cave in August in some countries and When We Were Young & Brave elsewhere in October.
Gaynor has collaborated with American author Heather Webb on Last Christmas in Paris (2017), Meet Me in Monaco (2019) featuring Grace Kelly, and Three Words for Goodbye (2021) (co-written over the COVID-19 lockdown).
[19] Gaynor runs the Inspiration Project, which conducts workshops for aspiring writers, with Catherine Ryan Howard and Carmel Harrington.