Some time ago I decided that Adrien would have a tomboyish girlfriend, because androgynous couples who share clothes are the cutest anything ever. I also decided that she'd be a fox, because fox and mouse is my favorite anthro pairing ever. I promptly did nothing at all with those decisions for several years.
More recently, Cladz posted a journal about how annoyed he is that fennec girls are so hard to come by in the fandom. This inspired me to make her a fennec instead of a red fox. I had Cladz draw her, and she came out super cute.
I mentally debated a couple of different names, and finally settled on Edna (but she goes by Eddie). Still brainstorming a last name for her.