Who sissy in deep and dark and dangerous?

she is the girl that was mean to ali and Emma. she is rude but later on she drowns at the same age as teressa. she is also hated the same way that teressa was hated because it says that linda and another woman used to always run away from Teresa because she was mean and hated by adults and children. Emma and ali are always hateing, and telling her to go away,sissy because she is mean and hated by them only. she is mysterious because no one around town knows about her ,she is hated the same way Teresa was, and she died the same death at the same age. sissy is so mean because delucie and clarie will not tell the truth about Teresa's death. and because of that that leads me to believe that sissy was Teresa's ghost and that is probably why Teresa was not found. BTW: READ THE BOOK IT IS WONDERFUL AND GREAT.