Baillie was born in Crawley, West Sussex, on 28 August 1981,[2][3] and she moved with her family at the age of eight to Filey, North Yorkshire.

[7] Baillie moved out of the family home at the age of 15[8] and left school two years later to work as a legal secretary in Reading, Berkshire.

As an opposition member she served on the Children, Schools and Families Scrutiny Committee and during the 2016–2017 civic year she chaired a review of mental health service provision for young people.

[27] In July 2021, Baillie commented that she opposed the removal of the Blackboy Clock in Stroud as she felt that it was important to leave all statues to "reflect our country's journey in the 20th and 21st centuries toward equality" but supported adding "factual information" on the "origins of its imagery".

[29][30] She apologised in August 2023 for wrongfully claiming that she had created the Natural History GCSE on her website and in a campaign leaflet.