Hi, I would suggest trying simplest things first. I believe a shot like this could be done by a northern window provided you can get some distance to a dark background that’s not lit by the window. You should try to get her as close to the window as possible to increase the contrast between subject/background. An open door to a room without windows/lightsources could provide a good background. Another possible background is a wall a few meters from the window covered with black fabric.

Depending on how well you’re able to separate the light to the subject from the background, you may get some detail in the dark background. This can be made entirely black with blackpoint adjustment (levels) and/or local adjustments in post processing.

(This is how I would try to do it without owning any large softbox. But of course, if you have access to professional light modification gear it could make things easier.)