She married Jan Cornelius van Boumann in 1884 and, at age 22, they moved to The Hague where her husband took work in the Dutch Finance department.

[1] She became involved in Dutch artistic community and met photographer George Hendrik Breitner and painter Isaac Israëls among others.

[2] in 1898 de Lange helped organise an exhibition of women's labour in The Hague, for which Jan Toorop designed the poster and catalogue.

[1][2] In 1899, as an outcome of the exhibition, de Lange founded and hosted the meetings of the Vereeniging voor Verbetering van Vrouwenkleeding [nl] (aka "V.v.V.v.V", the Association for the improvement of women's clothing).

[2] In 1902 there was a split between those who wanted to concentrate on the working woman and those who thought that reform was mainly required for those who spent some funds on fashionable but restrictive clothing.