Tween Troubles

I'm having issues with my tween daughter. I absolutely love her, and she is a great kid. But she is driving me crazy! and I don't know the best way to handle it.

For some background information... she is adopted. Which, to me, does not mean that she's any less my daughter. It was a family adoption- she's our niece. Her mother had given up her parental rights without checking with any family, so we had to go through the entire adoption process, which was completely grueling, but absolutely worth it. She's been with us since she was 5. We did not know much about her living situation until after we had her living with us full time and got some paperwork/background info from the state. She had been in and out of foster homes and had spent much time with babysitters and fending for herself at home. Her past experiences had left her very independent. From the day she stepped into our lives she has struggled for control over just about everything. Fortunately, this seems to be one of the only somewhat negative behaviors she has (I say somewhat, because it's not always a negative behavior).

The first Halloween she was with us, she cried and was horribly upset because we would not hand her a knife and let her carve her own pumpkin (we let her draw the design for us to cut out).

Since day 1 we have had constant battles over her need for absolute independence. I have yet to figure out the best way to handle it.

Now she is 11. And she is constantly racing me to do things! When it's dinner time she will run around the kitchen trying to get everything we need onto the table before I get a chance to do so, or before I can tell her to stop, or before I can even ask her to do something.
She will abandon anything else that she happens to be in the middle of to do so (ie: feeding the baby). Now I certainly don't mind her helping out, but I would prefer that she be asked to do something before just racing to do it. And the big issue with her being in such a hurry is that she will end up spilling things, knocking things over, or making a big mess in the process.

Every single time that we have left her at home with a babysitter we come home to a big mess. Unfortunately the person we use to come watch the kids once in a while totally indulges her and lets her be in charge.

I do let her help me with things a lot. She loves baking, so as a special thing for her and I to do together we will make cookies or some other baking project. But honestly, it always turns into a big fiasco. She tries too hard to do things too fast, and tries to grab the next ingredient before she's even finished with the first one... I've explained to her and talked to her about taking her time and concentrating on what she's doing, but it has made no difference. I'm at a loss.

While I appreciate (and to be honest, sometimes take advantage of) her helping with the two little ones, she tends to go above and beyond some boundaries when it comes to their care. Which is to say she will do things for them and give things to them without asking (ie: getting their bottles/cups, changing diapers, giving them food/cookies-whatever it is she thinks they need, run to pick up the baby when I am sitting right there). Now, I am a big control freak, so that totally gets under my skin. And there's not really a nice way to tell her that. I have explained to her the importance of not giving the baby any food without asking first. And I realize that in all likelihood she is just trying to help. But it really makes me angry when one of the little ones has a sinky butt and she races me to the diaper/wipes stash. It makes me think that it is all about control for her. It's apparent that she wants to be in control of every aspect of her own life, and it annoys her to no end when we treat her as if she's a child (read: when we treat her as a child of her own age). But she really needs to understand that I am the parent and that I'm the one in charge.

Am I just paranoid here?

I know that things are just going to get worse from here on out, as she's not even a teenager yet. So I'm really hoping to get some kind of handle on this situation soon.