Her Liberal Wesleyan Methodist parents were Mary Ann (born Bamford) and Thomas Slack.

Her father made bricks and her elder brother, John Bamford Slack, would become a minister and politician.

[1] Slack had good connections with the American Woman's Christian Temperance Union and she referred to their President, Lillian Stevens as "mother".

She continued her education afterwards attending summer schools at Oxford and Cambridge in bible studies before the First World War.

[1] The following year, her niece Aelfrida Tillyard, published the first biography of her life, documenting her travels to Canada, America, Scandinavia and South Africa.