First of all, I personally don't mind Katie Holmes...but it would be great, since we will likely never see Barbara Gordon or Batgirl if Joker did to Rachel what he did to Barbara in The Killing Joke.
Think about it, Batman can save Rachel...Joker can witness it and he abducts her, tortures her until she reveal's Bruce's true identity (because it seems like a trade mark of comic films that the villian has to find out by the end), takes pictures of her being tortured (and even killed) and leaves them right on Bruce's door step.