In the credit page of Guilty album....
 

So in the credit part of the guilty album she wrote that "This album is dedicated to a dearest person. May she rest in peace.... 1997~2007" Who is she talking about??

Check out this thread:

http://www.ahsforum.com/forum/showthread.php?t=67516

Seems very likely it's that Natsuki person, though there is no 100% undeniable proof that it truly is. Of course, if you say this to some people on this site, you will get snarky responses. I just think it's better not to state things as fact until you honestly know it's a fact.

EDIT: Dang, you beat me to it, Alternarist~! xD