Some of her fellow unicorns whom we’ve seen thus far do wear clothes (at least on occasion), such as shorts, shirts, robes, bathing suits, and vests. Maybe the laundry she’s referring to belongs to Lord Splendid Humility (although I suspect he’d be w-a-y too humble to let another unicorn do his laundry for him), Clip Clop, or maybe even her sister Florence. If Marigold is particularly good at it (such that the items have a magical sheen, say), I can see her doing it—especially for Florence—as a matter of pride.
Some of her fellow unicorns whom we’ve seen thus far do wear clothes (at least on occasion), such as shorts, shirts, robes, bathing suits, and vests. Maybe the laundry she’s referring to belongs to Lord Splendid Humility (although I suspect he’d be w-a-y too humble to let another unicorn do his laundry for him), Clip Clop, or maybe even her sister Florence. If Marigold is particularly good at it (such that the items have a magical sheen, say), I can see her doing it—especially for Florence—as a matter of pride.