Maybe the Nightmare aspects don't have to be that difficult to manage or write. I've been thinking about how some of them could have an impact on the bathtub-scene.
A PC has a Nightmare called "Drowning in dark water" - this is how it could affect the scene.
As the PCs approach the woman in the bathtub, the water slowly becomes darker and darker. The woman in the tub is completely submerged and doesn't move until a PC comes close to her; she then starts to move around violently in the water, dragging the closest PC into the water (skill check to avoid drowning). The aspect has been applied to the scene, and will follow the pcs until it is removed. Any scene can now potentially include the themes dark water and drowning. It shouldn't be overdone; the aspect might lie dormant for several scenes, but the GM should note all active Nightmare aspects and apply them only to enhance the action and atmosphere.
As the players move on, more and more Nightmare aspects may come into play, affecting the scenes until a climax is reached or the pcs remove all the aspects.
Other Nightmare aspects could be "What's hiding in those shadows?", "Everybody is lying to me", "Bad things behind closed doors"...
