Well, it could be that there's a magical artifact that has a side effect of making things around it wet. Ladybug comes in contact with it during a mission. As she tries to retrieve it, she gets drenched. This leads to some funny moments as Chat Noir teases her a bit about it. Meanwhile, she has to focus on the real task at hand, which is to keep the artifact safe from the villains who are also after it.
One idea could be a scenario where Ladybug gets caught in a sudden rainstorm during a battle. Her suit gets soaked and she has to figure out how to keep fighting effectively while being wet and a bit hindered. Another could be a beach episode in the fanfiction world, where Ladybug and Chat Noir are on a beach mission and Ladybug has some sort of water - related mishap that makes her 'wet for me' in a comical yet in - character way.
Perhaps there could be a plot where an akuma has the power to create water - based illusions. Ladybug is constantly tricked by these illusions and ends up getting wet multiple times. This could add an element of mystery as she tries to figure out how to defeat the akuma while dealing with being wet and the distractions it causes. And also, a story where Ladybug accidentally falls into a pool while chasing an akuma, and then has to deal with the wet suit and her clumsy situation while still being the hero.