Seriously falling out of love with my 3yo

[Runmumrun1]

On here it at least seems like I'm not alone and that my loving, fun, darling daughter hasn't turned irreversibly into a monster! Her change has coincided with a new addition to the family (baby not pet!) but doesn't seem directed at her although I'm sure it has played it's part.
We seem to battle over everything, even when we're about to go out for a nice morning eg. This morning she wouldn't get changed (just ran around the room) and she deliberately scratched me. Getting angry just inflames the situation so I (try) to keep calm and manipulate her into cooperation. I feel like I should punish her bad behaviour, such as being rude, scratching, hitting etc but always find its counterproductive. She gets lots of praise for being good and I've tried to introduce a reward chart for her but that's very hit and miss.
What is the one piece of advice you'd offer for me? I've heard the 'pick your battles' and that's very wise!
I know it's a phase and that she'll grow out of it but I'd like to try and manage it in the best way in the meantime!
:-)

See it as a positive developmental step. Developmentally appropriate and developmentally necessary for her to become an independent adult many years from now.

I think you may be sending her mixed signals about who is the boss. She knows she can win sometimes and you will back down. It is not really that she wins but SHE thinks she does and this enforces the behavior more. If it is the baby maybe get her to help more and feel more apart of that with you. If she bite or scratches does she still get fun even if it after she apologizes? I would cut that out completely. When you see she is getting upset get don't keep it up until she hit or does something rash. Get up walk out of the room and tell her it is time to kool off. If she persist on the nastiness then you need to stand firm with punishment, no desert means no desert. make her favorite that night. That will let her know there are consequences. All the things you are doing seem awesome! I love the rewards chart thing and that may take time for her to really understand rewards. I think at this time she needs to have it more simple. No tv or whatever she likes. Let her stay in her room and cry it out. Their should still be a punishment that is set in affect the minute she acts out. You don't want to be the mum picking you kid up from school cuz she popped or bit someone.