Part of this could be her age, because she's trying to "find" herself as an autonomous person. Part of it could be changes in family dynamics with the baby and the kinds of time and attention you can now give her.
Unfortunately, you can't "make" anyone, adult or child, change their actual feelings. Punishment may actually make matters worse, because something she perceives she needs is not only going wanting, but she's receiving negative consequences for having that unmet need.
I'm not there to hear the actual tone of things as your daughter expresses them, but I'm guessing she's feeling uncertain about her place in the family and in your heart, even if she adores her new baby brother. This is a huge change for her, and a few months ago she may have had to acknowledge that she's not the only child anymore. She may have changes going on in her educational life, as well, or the patterns of her friendships, that are puzzling or frustrating her.
If you were to quietly contemplate life from your daughter's point of view, and noticed that Mom and Dad were much busier and more stressed now, and wondered whether they still loved you as much, might you push buttons to see what happens? If you do something annoying, and Mom reassures you that she loves you, wants your happiness, AND hopes you will play your part in keeping the family running smoothly, how would that sit with you compared to Mom getting annoyed or impatient with you and sending you to your room? What would continued punishment do to your desire to contribute positively to your family?
Something that children your daughter's age are capable of comprehending, with some helpful coaching from parents, is that they are capable and original problem-solvers, and can be appreciated for those budding skills.
This is a real hit of the power and control your daughter might be craving right now, and once she tastes it, she'll want more. So I hope you'll read the wise and practical book, How to Talk So Kids Will Listen, and Listen So Kids Will Talk, by Faber and Mazlish. It will equip you to know when to talk and when to listen, how to draw your daughter out so you know just what's going on with her, and how to assist her in some creative problem-solving. All in easy to read, easy to understand and implement steps.
You may end up wondering how you got this far without this wonderful resource. It's my favorite parenting book ever, and I've watched it do some amazing things in young families with problems like yours.