Oooh, sorry, D.Gray-Man.
And yeah, you're pretty much right on. Though I'm not sure if Griffith
had to do it (since he was already re-born), or if it was just some sort of "revenge".
Casca and Griffith were the sacrifices to make him the 5th member of godhand, thus they were branded, and the other members were food for the monsters of the eclipse. I'd suppose he raped her out of spite towards Guts, who apparently "ruined everything" by leaving the Hawks after the war was over, and it probably had alot to do with the conversation that he over-heard that caused him to try to run away with the carriage, and him realizing how weak he was.
And I do believe she'll get her mind and voice back, and it should be fairly soon (if you're caught up to the current chapter you'll know why). Its just taken a long time as Guts and Casca are both branded and are both always haunted by demons and monsters and everything inbetween.
Casca is awesome. I can't wait for her to get her mind back.