I've been through similar situations. Even in third grade! Don't worry, you're not the only one here that goes through this everyday.
In third grade my best friend and I wanted to start a 'club' with our other friends. So we did, but she wanted to be 'Leader 1'. Everyone else voted who was to be Leader #__. All the while I was telling them that it wasn't fair to all of us in some way. Anyway, my best friend got voted Leader 1 and I was voted Leader 3. Anyway, in the end I ended up getting a couple of the friends that agreed with me and walking away, making our own 'club' where everyone was equal. She wouldn't talk to me. So I walked over there and confronted her that it wasn't fair to have leaders and that we should just quit the whole club thing. You might do the same? Tell her how she's acting from your point of view, and everyone else's.
Ever since my other friend's birthday party she's had a big head. She thinks she can just tell everyone what to do and tell them to shut up. She's been asking me if she can hit the new kid, and every time I tell her to leave him alone, because he's got it hard enough as it is. She tells everyone to shut up whenever she can. I'm getting tired of it. So Tuesday (we have a four day weekend that's half over) I'm going to tell her that she's being bossy and she needs to stop, because nobody likes a bossy-pants (XD). I think you could do it too!
I hope I helped! Good luck.
Maybe you can talk to her new best friend and see if you can go from there. If her new friend will talk to her, that could help.
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