Talk

She's a middle child.. Eldest is four and I have this with her sometimes but not as bad.

And a one year old who has my attention too

And the worst this is like today we've had the morning from hell where I've resulted in raiding my voice loads. I'm almost in tears and she has forgotten about the horrific morning.

All of this. For me trying to get them ready to take them to playgroup.

I just don't know why I bother on days like these

Feeling guilty for shouting

But she just doesn't listen.

* not all the time but a lot of the time recently.

If you shout - then she won't 'listen' It just escalates a situation.
If you tell her not to do something - why are you trying to make it fun?? If you mean it then it is serious. You could be giving her mixed messages, You mean it - but don't sound like you do?
Her anger probably does from frustration she cannot handle so you need to stay calm yourself to have any hope of calming your DD.
It is best to speak more quietly and go over to her and repeat what you have said and do not react to her getting angry by flaring up yourself.