Desna is Goddess of travelers. It seems possible that she might call a Paladin or two, on an individual basis, to protect travelers. Even if he personally has a Lawful philosophy. He might be in the final stages of his training at an order of Iomedae, when Desna begins entering his dreams and calling him to her service. Butterflies would begin to pester him during his sword training and meditation. Eventually, irritated, he would relent and leave the service of Iomedae to wander the earth helping travelers in need that Desna guides him to. Belonging to no Order. Just one lonely little Pally with prophetic dreams and a calling. He probably grumbles quite a bit at his Godess's chaotic nature, maybe even resents that he was chosen by her, but consoles himself with the good that he can do. A Chaotic Goddess would certainly be within her nature to call a Lawful character to her service, that's a pretty chaotic thing to do lol, and her ultimate reasons for doing so can remain mysterious. But what Paladin could turn down a divine call to protect innocents in peril? And it's not like she is ordering him to "Go Forth and Sow Chaos!" She's not actively working towards anarchy, she is just a little flighty ;) I think the idea of a CG hippy-chick Dream/Butterfly/Luck Goddess choosing a stodgy by-the-book LG Paladin as a champion, against his will, presents great (and hilarious) roleplaying material. I mean that's basically the tv show "Dharma and Greg". Inner conflict with one's own calling and one's own deity is a roleplaying gold mine. The trick is, he has to really lean into the "Good" and try to ignore the "Chaotic" nature of Desna. He must remain true to himself, in spite of this mysterious cosmic force that plucked him unwillingly out of his comfort zone, and try to make the best of it. To do good, in an orderly fashion, for an unorderly deity. To remain a true and steady Paladin IN SPITE of his Goddess, not because of her. Because sometimes you choose a God, sometimes a God chooses you.
-Bastion Ambrose, Paladin of Desna