You open the mirror and find many toothbrushes, each of a different color. Each color matches the color of one of the rooms in the upstairs area, minus the black and dark gray colors that belonged to the Changelings and the greenish-blue that belongs to the EMH. You assume each toothbrush belongs to the occupant of the room it matches.
You close the mirror and notice in the reflection that the shower seems to have moved from wall to wall and magically changed shape. When you turn, you notice there are actually two showers, though your previous theory isn't a bad one for this house. The shower across from the mirror is large with a large tub, complete with cream curtains. The one across from the door is much smaller and is only a square shower unit built into the wall with a frosted glass door and cream tiles.
As in the bathroom downstairs there are stenciled pictures on the walls, though up here only a small, deep-green seaweed pattern crawls across the top of the walls. The rest of the bathroom is colored in cream and white colors, the counters flecked with gold paint.