Rosalina now has two tattoos because I said so. On her upper back, spanning across her shoulder blades, a large tattoo resides, looking like a mixture of these two tattoos here and here. A moon with its smooth curve facing downward sits centered in a field of constellations, smaller groves of stars clustered around the larger connections. It takes up a considerable portion of her back, but the moon part is the only bit commonly seen, thanks to her shoulderless dress. Otherwise, a different outfit will be needed to see the entire thing.
Her second one is a sleeve down her left arm. Again, often covered, but viewable if wearing a different type of outfit. It’s a scene of variously-sized shooting stars, coating her arm from below the shoulder to a little before her wrist. Some are connected by lines to form more constellations, though most simply looking like a starry night sky.
Rosalina’s natural magic has worked its way into the stars, too, having them give off a separate light glow like her body does as well. It’s far from seeable in the day, but at night, or a particularly dark setting, the tattoos underneath her clothes can shine through and appear visually.