Charetor development.
Serena: what is that?
See? Clueless. She doesn't even know!
Serena has none! She's just the girl who traveled because of the boy she loved. Nice lesson to teach pokemon!
Misty travels because of her bike
So did May and dawn Iris traveled because she helped ash and they became friends!
But Serena? She traveled because she liked hIm.
Wow.
Just wow.
-.-
The only charecter development she has is that she's a bad character in general!