Do you know the title of this book?

i can't remember the title but its about this girl who gets sent to Louisiana by her dad to live with her "aunt" that's what she called her even though they aren't really related and she wonders into this cemetery one night and becomes friends with this girl who's name i believe is Helena or Helen though i'm not sure and the girl she become friends with turns out to be a ghost who haunts the cemetery the girl who gets sent to Louisiana also has to live with her "cousin" who is the daughter of the aunt and she has to attend this one boarding school where they where uniforms