"Mrs. Granger," Severus said quietly.  "I understand, but I was... familiar with the tactics used by the D..." he sighed.  "By Voldemort during the war.  Had Hermione not erased your memories of her there is no question he’d have used you as a means to find out where Mr. Potter had gone, even if you knew nothing of where your daughter was when she was traveling with him.  She meant to protect you."