Out of all the users in Miraculous Ladybug, few can say that they were made specifically for their partner Miraculous. While there have been other users of the Ladybug Miraculous in the past and present, Marinette seems to be the best choice for the earrings. But why is this?
The key is in how she uses her powers. Almost every episode of Miraculous has Marinette receiving an item from her Miraculous via her Lucky Charm ability. The only drawback is that the solution for using the item isn't always clear and she usually has to figure out how to use the given item herself. This is where she really shines, as she's always able to find creative ways to use the item in order to take down opponents. It makes sense given that Marinette is an artist who aspires to be a fashion designer one day. Her mind is trained to think creatively and out of the box naturally. This is what gives her an edge in fights as the Ladybug Miraculous holder, as she is the one who most successfully taps into the creative power of the earrings.
To emphasize this visually, whenever she looks around to see what the item is used for, the viewer sees a greyscale version of the surroundings with the solution lit up in ladybug spots. While this may seem like the Miraculous telling Marinette how to use the item, one could argue that this is Marinette's brain at work instead. It isn't the Miraculous, but the user figuring out the solution.
We've seen someone else wield the Ladybug Miraculous in the show. In the Season 3 episode, "Reflekdoll," Adrien (aka Cat Noir) temporarily used it while Marinette used his Cat Miraculous. As Mister Bug, he believed that he could take down the akumatized Reflekta in the same manner as the duo did the last time they fought her, and, surprisingly, was given the mirror he desired from the Lucky Charm to repeat their success. But Lady Noir explained that it doesn't work like that -- the solution isn't so easy to find. She was right, as reflecting the beams from the Reflekdoll only made it more aggressive. Instead, they had to use a mirror-like screwdriver to open a panel on the back of Reflekdoll's head in order to get inside.
So while Mister Bug got the item he wanted, he just couldn't use it how he wanted. When he looked around for the solution, everything was in greyscale but there were no spots shown. This could further the idea that the spots appear as a result of Marinette's creativity and problem-solving skills rather than the Miraculous helping its wielder.
As a would-be designer, Marinette has to be creative and come up with new ideas, sometimes on the fly. This is her biggest strength as a Miraculous user because sometimes the solution to a situation may be more complicated than it first appears. Cat Noir, on the other hand, likes to fight things head-on and look for the simplest and more direct resolutions, whereas Ladybug is more creative and tries to see things from different points of view. This is why he couldn't see how to use the mirror when fighting Reflekta for the second time. Therefore, because of her quick-thinking and creative solutions, Marinette, and no one else, seems to be the perfect fit for the Ladybug Miraculous.
