mmm i think bella has always been mature in the ways she shows maturity in this book. i have been one of the people who say she shows very little maturity, and i still find her to be highly immature. although that is still based on the previous three books, not BD. in BD, her maturity wasn't tested in nearly the same ways as Eclipse and New Moon. however, when it was, her lack of it showed.
for instance, in the beginning, before the wedding, before jake comes back, when bella is worried about him, she continually talks about how she will miss "her best man" and how there will be "an empty seat at the wedding" and just basically feeling sorry for herself. i wanted to wring her neck. she wasn't even going to invite him to the wedding! edward had to send the invitation behind her back! it just seemed very self-centered to me.
and then again, when she was pregnant, well let's just say that i was so proud of leah for standing up for jake.
and then AGAIN, when she found out that jacob had imprinted on renesmee, and she basically attacked him. it wasn't his fault! he had no control over it! of all people, SHE should know that! it was quite unfair. i don't blame her for being upset, not at all. i just think it shows that she's still self centered and immature, for taking it out on him. it was not even a maternal instinct, since she was upset, not out of fear for nessie, but she was furious because "already, nessie didn't only belong to me". selfish much?
HOWEVER, there were some things about her in this book that i thought were much improved. her communication with edward, for instance, made me so happy. i think once they were married, and she knew he wouldn't leave her, a lot of her insecurities vanished, and so she could yell at him and tell him how it really was, without being so timid. and that i really liked.
i also loved her determination to master her power.
and then the plan she made for nessie and jake, i was so proud of her. THAT was very mature and grown up, and she did it all on her own.
death cannot stop true love, it can only delay it for a while...