Here is a post from December 30, 2006 entitled Emily the Rip-Off.:

Emily the Strange is fictional character whose introverted and disdainful personality has made her something of a countercultural icon (and a great way to sell marketable products to the trendy). Her franchise has churned out a lot of merchandise (clothes, toys, books, etc.)
But the character itself is almost an exact copy of another (less desperately nonconformist) character, Rosamond, from the children’s book series “Nate the Great”.

Here, a writer at “You Thought We Wouldn’t Notice” recognizes the similarity.
Here, the Laughing Squid summarizes reader comments on the similarities and quotes from the creator of Rosamond.
Here is the tex of the declaratory judgement action brought by the creator of Emily.