From Homestar Runner Wiki
Karen Chapman Wagner is one of The Brothers Chaps' sisters. She lives in Atlanta and is the official President of Operations for the Homestar Runner store. She is mentioned by Matt on Wired News Radio Interview - 23 Jun 2003, where he calls her "Director of E-Commerce". Matt Cake was a birthday greeting that was sent to Karen. The link to Matt Cake originally appeared on the Strong Bad's Message Bored as a birthday greeting from Matt to Karen. This greeting featured Little Girl. At the time that this message appeared, Karen was a regular poster on this message board.
Karen is Little Girl's mother, and writer of If I Ran the Camera.