Her teachers included Arthur Briët [nl], Dirk Herman Michaël Harting.

She was married to fellow artist Piet Slager jr. [nl] (1871-1938) with whom she had one child.

[2][3] Her work was included in the 1939 exhibition and sale Onze Kunst van Heden (Our Art of Today) at the Rijksmuseum in Amsterdam.

[2] She was a member of the Arti et Amicitiae and the Kunstenaarsvereniging Sint Lucas [nl].

[4] Suze Bergé-Slager, Slager-Velsen's daughter, established the Museum Slager in 's-Hertogenbosch.