@the_stegman: Even if Laurel is moody, she is hardly as moody as Oliver. How many episodes have we had him saying he can't let anyone into his life because they always get hurt? Or that he can't be two characters at once? If Laurel is sad that her sister was murdered, she is being moody; Oliver is just so chipper all the time.
I personally feel that Laurel has had an interesting development cycle. She was rather unimportant in season one, she didn't really serve a purpose in season two, and now she is finally starting to do something that doesn't involve Oliver, and that's nice.
Too bad people see her as being moody. She isn't even the one most shaken up by the death of her sister. Instead we focus on how Oliver is feeling about it and he attempts to find the killer. Let Laurel do that, and the while have her start training so she can become the character she is meant to be.