A teen girl whose family has died is sent to live with relatives (maiden aunts?) in a part of the United States that still follows more Scottish customs than American customs, including holidays, and she experiences major culture shock.  I believe the title character is named Ellen.  The cover shows her at the door wearing a shift mini-dress, so the novel probably was written in the late 1960s or early 1970s.  This novel is the first time I encountered the word “haggis.”