Toddler Dealing With New Baby

I just had my second daughter two weeks ago... My almost 2 year old seems to be having a hard time transitioning... She has been acting out so much with tantrums and crying about every little thing that doesn't go her way and she's been messing with things she knows are off limits. It doesn't matter how much I tell her no, when I'm not in the room, she does it anyway. My SO and I have been including her as much as possible to give her as much attention as we can so she won't feel like she's not important anymore, but it doesn't seem to be helping.. I'm pretty sure I say no at least a few hundred times a day... I was wondering if any of you mommies have multiple kids and have advice with how to get past this rebellious phase. Thank you