User blog comment:Menara/Thalia's official Art/@comment-67.8.199.242-20120903150528/@comment-3146930-20120903150825

Well it just might be. The picture was released in The Demigod Diaries, and the story Thalia was in took place before The Lightning Thief (chronologically speaking). So the image could be of Thalia before she became a Hunter of Artemis, possibly even before she became a tree.