They sketch.
It starts with a few basic aesthetic things, sample facades in a few styles. Gradually she starts working in Gothic Revival elements, a bit of Eastlake as well. It's a big thing, with two stories, a tower going up a third, a balcony or two, and a bay window in one spot. It's just a loose idea, at this point, but it looks lovely.
From there, she starts laying out rooms. The ground floor gets an enormous kitchen with a table, a nice dining room, a lounge, and a workshop. A basement below that has room for all sorts of storage, another workshop, and an empty-ish room for sparring or training or meditating. The upper floor gets an office, another workshop, a master suite with its own bathroom, two guest bedrooms, and another bathroom. The tower gets another workshop. Sizes and arrangements get tweaked a lot. The bay window gets attached to the lounge. One balcony gets put on the master suite, the other gets moved around between the workshop on that floor or the office or one of the guest bedrooms, before finally settling on the office. She vacillates on adding a skylight for a while before deciding against it, and just marking down lots of windows.
Probably at least an hour passes over the course of her sketching and refining.