Help!! How the hell to get your 4yo to do as they are told??!!?

[OhWhatAPalaver]

I am almost at the end of my very long and stretched tether! My dd simply ignores any of my requests for her to do anything, it's infuriating and highly embarrassing in public. Eg, she wouldn't come and get dressed at swimming today, I had to try and run around after her and drag her back to the bench to get dressed! (not really running and not really dragging as I'm 35 weeks with dd2, which is making things much harder!)
She end up screaming, shouting, hitting and kicking and I was getting more and more annoyed with her, which didn't help.
She also screams very very loud indeed. I always think I look like a really terrible parent :(
I can't physically restrain her anymore either as she's very strong, her hits and kicks really hurt.
I felt terrible today as when she tried to run away again and I grabbed her wrist to try and stop her and she fell and hurt herself, which she screamed about very loudly for a long time. She then proceeded to hit and kick me several times while I tried to get her shoes on. Needless to say we left the changing room in a hurry. I feel really bad.
Part of the problem is my frustration, the fact that I could ask her to do something a hundred times and she would still ignore me really gets to me. She almost always does as her step-dad says straight away, although even he has been tested recently.
I don't know how I'm going to cope with a newborn and my 4yo behaving this badly, please help!!

[Believeitornot]

Try a bit of natural consequences. So if she doesn't get dress, so be it. Just leave and take her home. She will soon change her mind. Don't get cross with her, just explain the logic.

I also find that giving a bit of advance warning helps. So I would say to my four year old "after this story, I'm going to brush your teeth". We finish the story and she lets me brush her teeth. If I say "DD I'm going to brush your teeth now", then there's no chance it'll happen without a fight. Overall she feels like she has some control and I get her teeth brushed.

Also are you bigging up the whole"new baby" thing. I wouldn't. It'll make her unsettled. Don't talk up her being a big sister etc etc.