suddenly we are all just strangers on the internet however my response was rather blunt and rushed and for that I do apologise.
You used a few words in your OP which I'm afraid have the effect of making me see red. My fault not yours.
In my personal experience parents who describe their children as spirited and worry about 'crushing their spirit' are often a bit lax in the area of discipline and we've had some horrible experiences as a result.
Of course this doesn't apply everyone, and the fact that you are seeking solutions speaks well of you. I should have been more patient.
Speaking constructively
here are some thoughts:
In my experience there are two things which are critical to managing behaviour: tone of voice and consistency.
Tone of voice - you have to sound like you really mean it. That doesn't mean shouting or even raising your voice. A very firm, low tone. The kind of tone a really good teacher uses. I get so irritated by parents who say all the 'right' things but say them in a 'nicey' sing songy voice which is completely lost on the child.
You also need to clearly distinguish between times when you are prepared to negotiate and times you are not. So sometimes 5 more minutes TV is ok and sometimes you need to leave for school or an appointment and it's not. We have a stock phrase 'I've said no please don't ask again' which lets them know the difference.
Consistency:
It doesn't matter what your boundaries (everyone has their own) are just that you stick to them. You and your DP/DH need to agree on them together. Children feel more secure with rules and boundaries.
They also need to know who is in charge. Of course families discuss things and children should input to many decisions/give their opinions but in the end Mummy and Daddy make the decision and it won't always be what the child wants.
Other things we've found useful:
If the children misbehaved in public/in front of other people I always found it useful to remove them front the room briefly to speak to them. It gives you both some space. I find the 'this is not acceptable behaviour (followed by an explanation of why not) and I'm very disappointed in your behaviour today. I then remind them of what I would expect to see instead, get an apology and a hug and then go quietly back into the room.
I usually take five minutes in the car before going into a party or play date to remind them about sharing/saying please and thank you or whatever is relevant.
Lots of praise for good behaviour and occasional treats for extremely good behaviour (not in a bribery way but as a surprise).
Different children respond to different types if consequences there's no easy fix to that I'm afraid but if she's 4 there must be things she enjoys doing that could work (swimming in a Saturday if you are good/losing TV privileges/ losing a specific toy or opportunity. Or possibly a chore round the house. Often you being clearly angry/disappointed in them is enough to get the message across (and I don't mean shouting)
To go back to what I said in my earlier email, you won't crush her spirit or make her meek. You'd have to be actually abusive to do that and there is a massive difference between being firm or even strict and anything that would harm your child. However I firmly believe that a well behaved child is a happy child.
Good luck with your DD, 4 is often a difficult age.