Looks like a Case for Nate the Great

GalleyCat ran these side-by-side images from Nate the Great Goes Undercover (1974) and what the L. A. Times reported was the first appearance of a character named "Emily the Strange" in 1991.

The similarity was first documented by a sharp-eyed RISD student named Chelsea McAlarney on the website called You Thought We Wouldn't Notice, dedicated to cataloguing curious, uncredited similarities between samples of visual art. Al Sweigart at CoffeeGhost noted some other parallels between Rosamund and Emily in 2006.

Emily and her cats have reportedly appeared lots of Goth merchandise--not that I'd ever heard of her before. Apparently nihilism is big business. More recently, GalleyCat says, Emily has inspired comics and an upcoming series of YA novels.

The Nate the Great series was written by Marjorie Weinman Sharmat and illustrated first by Marc Simont, who are no doubt in touch with their representatives.