I'll preface this saying I have no experience with adopted children , but I do work with children and a lot of them have suffered trauma, have SEN, social and emotional difficulties , ODD, attachment disorders etc.
I would say first of all pick your battles. It sounds so daft when you say it, but a lot of parents /educators get so hung up on a billion things children simply must do. As long as it's not harming them , let them have some leeway and have a few clear and non negotiable "musts".
Second ,I might be teaching you how to suck eggs but have you tried closed choices. Like in the park example.. "do you want to go to the park now or later?" , "do you want to wear your wellies or trainers to the park?" . Basically the park is a given, but she has choices over how/when she gets there. Always try to keep it to two choices(three the most) and they must be choices you are happy with. Sometimes she might throw you a curveball and say "sandals" or whatever. If it's suitable, just roll with it.
With this give her constant warning so 30 minutes left, 15 minutes, 5 minutes ,1 minute. Or use a now and then approach. Now we'll do some colouring, then we'll get ready to go to the park. So they always know what's coming and they're ready for it.
Try and join in with the tasks you ask her to do. Make it a "team" activity "let's go get out shoes", "let's see what pasta you want for dinner " , "let's tidy up together ".
Adding "thank you" after asking her to do something can sometimes help, but I've only used it with older children . So like " please put your shoes away. Thank you".
As for natural consequences , that's harder for things where you rely on "missing out" for them to comply. Their attention span is too limited and they're too easily distracted to realise that right now they're missing out on something they enjoy.
Praise,praise ,praise and lots of attention when she does something right. Be specific so instead of "good girl" try "oh you were so quick getting ready", "you brushed your teeth so well", "thank you for listening/holding my hand straight away" etc.
You might already know/be doing all of this or maybe it's not suitable for an adopted child in which case I do apologise.