Here's some art from the original Chowder pitch I brought to Cartoon Network. Both characters changed pretty radically once the series began. Endive had a physical change, but Panini had a total rethinking. In fact, she was originally named Borlotti (a type of bean.) The first version of her design had pointy ears, but that didn't fit with the rounded, soft feel of the rest of the characters. She also had an outfit where only her face poked through.
In this stage, she was kind of mean and I thought of her as someone who would take advantage of Chowder to her own ends. She seemed like an Angelica from Rugrats. But then I realized I don't like those kind of characters. She needed to be cuter and sweeter. Once I figured out she'd have a crush on him, everything about her made sense. Not being of the age yet where he's into girls, she would cause Chowder plenty of consternation, but in a more fun way. And the new name seemed to suit her better.
Endive's character stayed pretty much the same, but became more of a triangle shape. The long nose was always there and was supposed to represent the way she would look down her nose at everyone. It was great to see her personality evolve naturally over the course of the series, especially when written by William Reiss. Now it's crazy trying to imagine if the two of them had stayed like this.