I'm Scared of my Troll Mother!

(from ebookjapan):
Sayaka and Kaori, who became sisters-in-law after their parents remarried, were living together happily. However, Sayaka's stepmother feels that Sayaka is superior to Kaori in everything, from her studies to her social life, and she keeps hexing her with black magic night after night. Soon, Sayaka's beautiful face gradually begins to disfigure and crumble..!　Kaori tries to break the curse somehow...