My heart goes out to you, I can just imagine how frustrated you must be.
Itsounds like she is testing boundaries and trying to figure out how much control she has, but from what you've said it's not what she really wants. Sounds like she's so focussed on the battle, but possibly what she really needs is the consistency you're trying to give her. She is just struggling against it for now. Or has this been going on for a long time?
Do you have set routine?
Maybe if you tell dd "in half an hour we are going to go outside (when the timer goes off, when the big hand is on the 12, whatever) but we can only stay out for an hour (again, I find "when the timer goes off" to be a brilliant tool, makes it indisputable) and then we have to come inside. lets put your jacket and shoes on now so that you are ready to collect the eggs. If she only comes out with 5 minutes to spare you still go in when the timer on your phone or whatever goes off, and she'll know for tomorrow.
It's hard when they make you so tense, it becomes impossible to enjoy them.
I'm guessing consistency is the key, and making sure she understands what is coming next at all times, but I don't know from experience. I hope someone else has words of wisdom for you.
Hugs and luck to you. Not looking forward to dd hitting this stage,