Not just one bathroom but many. Plural number. Every respectable mansion has at least a couple of guest bathrooms. The house where A. lives belongs to her grandparents. The mansion is kept in an old Victorian style and so are the rooms.
In the guest bathroom a person that happens to wander there will find all the basic toilette utensils like a fluffy, expensive towel, oriental scented miniature soap bars in various shapes, hand creams and even a disposable toothbrush along with minty toothpaste.
As for the color of the walls and furniture, the room is kept in subdued light tons of white and powder blue.