Whenever at all possible, you should do these things when writing a character:

• Make him/her as smart as possible
• Make him/her as active as possible

If your character is dumb because you need her to not figure out something until a later chapter, you're not writing it right. If your character is motionless because you can't figure out something for her to do when she's not "on stage" in your story, you're not writing it right.

Now, if you'll excuse me, I've got to go from Chapter 20 back to Chapter 2 and rewrite an entire character.