Un petit tour par la case maquillage et je suis toute pimpante, mais aussi très endormie, pour retrouver mon amoureux.
I don't understand the meaning of the nouns "tour" and "case" in this context, as well as if "maquillage" is an adjective.
It' a humourous way of putting "un petit moment à me maquiller"; it refers to a board game played by the French in the last century and probably still today; it is called "Le jeu de l'oie" (ref). In this game each of the squares corresponds to an activity and the speaker in her sentence identifies life to a series of activities well confined to compartments, as in the game.
"case" is "square"; "tour" is "turn"; as you throw dice in the game you get from one square to another.
The construction "case maquillage" is the common construction of compound nouns; it means "square where the make-up is applied".
Un tour, especially un petit tour, implies a detour from your primary purpose/goal. Not a major detour, especially if a petit one, but not where you were originally meaning to go.
La case is a box, or more generally a topic, an area of interest.
So here what you have is something like 'a small detour into the makeup area and I'm all spiffy, but very sleepy, to go meet my lover'.