Hour Three: the dark rooms
Nudge. Cross out every room whose light she has left on, and both doors. Then find the way that is left.
Harder
The boot room is lit, so you cannot go along the bottom row. Go up from the cellar stair instead.
The hour, in words
The plan is a grid of twelve rooms in three rows of four. Top row: Library, Hall, Dining room, Front door. Middle row: Still-room, Passage, Kitchen, Scullery. Bottom row: Cellar stair, Boot room, Larder, Back door. You start on the Cellar stair. Tap the next room you walk into, one step at a time, up, down, left or right; each tap is added to the line marked The way so far. Then tap Go to her. Back one undoes a step and Start again clears it.
The answer
The answer is a3-a2-b2-c2.
The library, hall, boot room and larder are lit and both doors are locked, so from the cellar stair the way is up into the still-room, across the passage and into the kitchen.