This is a bloody apple. The apple is a sign of temptation, suggesting the temptation for Grace to kill. It's also temptation of another kind, when Simon offers the starving Grace an apple and she is hiding her desire for it until she "lift(s) the apple up and press(es) it to (her) forehead" (42).
I can see you darling, showing all your scars but nobody pays attention, they are so blind by beauty that they don't know the ugly that is beneath it. I help you, I help get out and show your scars, tell them you're here