A.,
I think all children hit or bite or throw things or act aggressively at some time or another. I agree with 50% of Julie C's posting. I do not believe in spanking or hitting anyone or anything from my kids to my dogs. In MY opinion, it doesn't make sense to expect your child not to hit, while you hit them. I just don't get it. But, that's my thinking and it works in my house. As parents, we all need to figure out what works for our own kids.
My sister and I are 17 months apart and although we have a lot of similarities, my mom learned very early that what worked for discipline on me did not work on Michelle. One of our punishments was writing 50, 100, even 1000 times (I had to do it). I HATED it with a passion and the threat of having to "write" got me to straighten up really quick! My sister didn't care. She just wouldn't do it. She'd sit for days and draw pictures on the paper. My mom had to find out what DID work for her. It ended up being taking things away that worked.
My youngest sister (15) has always been very affected by my Mom shutting her out. Not talking to her, removing affection when she was nasty to my mom, etc. She's 15 now, so that's a whole different battle and not sure what works! Lol.
I think consistency is the key. If you decide to take away a toy every time she hits/kicks/pinches then you have to do it every single time. And your husband/partner has to do it, too. As soon as you slack on it, they know. My 2.5 year old son started spitting lately when he's mad. At first I ignored it, hoping that no attention to it would make the phase pass. But, he did it right in my face. So, I told my husband that from now on spitting = timeout. I also told my son this. And I mean it, too.
Although it seems you have tried everything, I would suggest maybe taking a day or two where you do the SAME thing. See how it works and effects her.
Finally, I will say that I had dinner with an old friend the other night and she had some severe issues with her son. She found out that food allergies were the culprit. I know it sounds far fetched, but she showed be before and after videos and the transformation was absolutely amazing. Amazing. If the aggressive behavior continues, I would suggest looking into that.
Good luck and I hope you can figure it out! I'm so sad to read your post.
T.
Oh, I wanted to add...I agree with Angela A. that praise is just as important as discipline. When my 2.5 year old shares or gives hugs/loves to his 4 month brother, I make sure to thank him for being so nice. When he's playing nicely with his Thomas Trains or Cars, I be sure to tell him how happy I am that he's playing so nice and I ask him to give me a "high five". He loves it and I think it works wonders. Ok I'll shut up now. Have a great Holiday!