Feel free to agree or disagree with this; it's just a thought.
Warning that this is 100% unedited and I don't plan on fixing it up anytime soon, so Grammar Nazis beware.
One question that still lingered in my head after playing SH2 was just what the purpose of Laura's being in Silent Hill was. Of course, she's there to give James another reason to be looking for Mary, but unlike him, Angela, and Eddie, there's no mention or hint that Silent Hill really "called" to Laura as it did to them. The case for Laura is the same for Maria--Silent Hill didn't "call" to her, either. We learn that it's because Maria isn't real, but a creation of Silent Hill. I realize that this may debatable with the "Maria" ending, but for the most part, just judging by all of the endings that passed Maria off as a creation of Silent Hill (outnumbering the "Maria" ending's speculation of Maria being a real woman), I'd say it'd be a strong possibility that the intention was for Maria not to be real.
Now, take the connection that Laura and Maria have, add in the fact of Maria being Silent Hill's creation, stir well, and then this thought comes up - what if Laura is also a creation of Silent Hill?
Yeah, Laura did share with James a letter written to her from Mary while she was in the hospital, but what if that letter wasn't real, either? Notice that in Mary's letter to James shown at the end of the game, there's no mention of Laura in it. Plus, if Mary and Laura had a close friendship, then surely Mary would have mentioned something to James about Laura or James could've walked in on them spending time together when visiting her. Not to mention Maria, who isn't real, says "I feel like it's up to me to protect her."
And consider this--connection is one of Silent Hill's themes. Just about everything around the characters is somehow connected to them whether it be about their past, their thoughts, or their feelings. In the case of James, Angela, and Eddie, they share the connection of all being real people (not just creations of Silent Hill) who all happened to have killed someone which eventually leads to them winding up in Silent Hill. They also represent the three tablets James finds in the Toluca Prison--the Pig, the Seductress, and the Opressor. Now, for a while I thought that it was Eddie, Angela, and Maria who represented these tablets, as Maria fit the "seductress" description far more than Angela did. However, when it's implied that Angela was sexually abused by her father in her past and that Maria isn't real, I immediately kicked this idea out the window.
We're given no indication that Laura and Maria killed someone. We're also given no indication that they were brought to Silent Hill. We're told nothing of their pasts (excluding Laura's possible friendship with Mary in the hospital). We don't find any tablets in Toluca Prison that represent them. Maria feels a great desire to protect Laura.
Coincidence? I think not.
I'm aware that Laura's seen in the "Leave" ending walking with James to Mary's grave, but assuming that it's the same graveyard where we first meet Angela that's by Silent Hill, what if Laura only appears around the Silent Hill area? Maybe not the best comeback to this, but it's still a thought.
As for Laura's overall purpose as Silent Hill's creation, I believe that she was made to represent either someone else who loved Mary and just what the impact of James' killing Mary had on her and thus having James coming to realization of how important his wife was, or to remind him of the hatred he once had for Mary through saying "You didn't love Mary anyway!" and just being all-around frustrating (and annoying) for James to handle despite her just being a seemingly harmless girl, just as it was frustrating to handle seeing the different side of a seemingly harmless Mary. (I could be very wrong on both of these and there's probably better theories out there on this, but I once again, they're just thoughts of mine.)