I have one of those....and let me tell you hang in there! Just give her the attention that she's craving at this time since she basically might believe she's been replaced by the baby. Like I said don't worry, by you paying special attention to her and reassuring her that she's still very important her attitude would change, but don't be surprised if once in a while she acts up again. Be patient and remember that this too shall pass! I can identify with you since I have a daughter (who's a twin with a boy), so as soon as she started talking she would not or could not stay silent. She had to say what's in her mind, the whatevers, and rolling of the eyes when she heard something that was for her so obvious or ridiculous, etc. So, I started telling her that as a mom it was my responsibility to guide her, tell her, scold her and adviser her, even if she already knew it (or thought she knew it) I still tell her that, and that I feel better if I say it just to make sure there's no misunderstandings...it has worked so far and she has turned into a beautiful, well mannered little lady, makes good grades, a very popular loving and kind friend, but do not step in her territory, or else. She is my hospitable child and stand for the weak kind of person. Our girls would be the ones standing for unjustice and won't be afraid to stand with the ones that stand alone, they will stand up to anyone, and I mean anyone if they see fit in any circumstance. I'm very proud of her and you will too!
If your girl like to talk she might also love to write, buy her a journal and let her write stories. I noticed that the talkative part equals a very active brain, so let her be creative with crayolas, legos, puzzles and like I said, writing....take advantage of her personality and find out her strengths!
My daughter is 14 now, but we had our rocky atitude years between 7 and 13....now, she's blossomed and the best thing I did was treat her as a "what she believe she was"(older & mature), so accordingly I gave her matching responsibilities and punishments. It worked, but don't forget that every child is its own person who desires most of all to be loved, heard and understood. I used to tell her that I was for her not against her. That I was in her team and not the enemy. That Daddy was someone that had the last word and she better learned obedience or suffer the consecuences. We went through lies, fits of rage, the unfairness of it all and are here to tell you it will get better, but you need to be consistantly loving and firm. Know her friends and family..stay connected. Make teachers your allies, involve family or a trusted adult to reaffirm your parental positions and values...it will be at the end of the day a good investment on your kid behalf.