When we tried to explain things, she would mostly just ignore our words and change the subject. There was even a period of time where even mentioning "baby" would cause her to yell "NO BABY!".
BTW, you might have heard of the "terrible twos". But the "threenager" stage was much worse for us.
Some of the defiance is kinda funny, depending upon your sense of humor. Like when my wife said "I hope when you get older you call mommy to tell her how much you love her", and she said "I'm going to call you to tell you how much I don't love you."
It's a lot better now, but she has always been pretty persistent and strong willed. At the end of the day, you get what you get. We have some friends with the most amazingly behaved first child that didn't care for our kid's behavior and some of the stuff we just let her do. Then their second kid was more like ours and after that they had more sympathy.
Did you smack her?
Worked first time to stop a child running on to the road for me, never needed to repeat it. Other kids in my care have learnt without that necessity, thankfully.
The twins bite her when she does something they don't like. Doesn't stop her from doing those things they don't like either.
We ran into this problem. Our oldest would just hit him again 5 minutes after the timeout. It got to the point where she would hit him, say "timeout!" and go to her timeout spot. She hated the timeout (she cried during it), but she decided it was worth it.
She basically took every chance she could to hurt him. If she was walking by him, she would purposefully step on his fingers. Or hip check him. Or smack him on top of his head.
We tried pretty much everything, and nothing worked. Ultimately she grew out of the behavior after about 8 months.