Hello - if you're still watching this post-our DD is semi-adopted - in that I am with her birth father (for about 2 years now) and as her mum died when she was 8 months I have now 'become' her second mummy. She's now almost 4 and she only really kicks off with me and him.
I think all children of her age are like this to some extent - its a question of degrees maybe -but I would advise that, whether its 'attachment issues' or not, you try not to dwell too much on that. Many birth parents have difficulties too, due to post natal depression, practical problems, their own struggle with becoming parents. Though of course its right to maintain an awareness that her security/attachment needs are very likely to be more extreme, I'm not sure the techniques need to be any different or that it means you can't expect to have a close loving relationship with her.
So by all means get specific adopter support, (I've not had any myself as I don't fit anyone's criteria!) but at the same time just try use more generic 'parenting' approach to do what feels comfortable for you, bcs that's the easiest way to be consistent.
I'm no expert but would agree with earlier poster to err on the nurturing side, let her know she's safe - but this doesn't have to mean spoiling her - just that when she can't have her own way, you can still empathise with her, let her know you understand how she's feeling, and you're sorry but things need to be this way (whatever that is). Suppose what I'm saying is you can be firm and have boundaries without being strict/harsh. In fact some people theorise that the boundaries make children feel safer, knowing there's someone in control. she's of an age where she can start learning to make decisions but maybe you can define what they are -eg choosing what to wear, park or library, what bedtime book to read.
My mum was widowed when i was very small and as a toddler i gave her a really hard time, to the extent her friends commented on how horrible i was to her . She once asked me why i was being so mean and apparently i said, if i can't be horrible to you mummy, who can i be horrible to? My mum took this as a kind of complement... and while i don't know the extent of your dd's behaviour and whether its extreme or not, maybe it would help to bear in mind that in fact its possible you are the only person she feels 'safe' behaving like this to - so try to remember that and not break that trust. At the same time please be gentle with yourself if/when you lose your rag occasionally. If i'm sounding a bit too good to be true here by the way, I had a bad weekend recently when I shouted too much at her - then felt so guilty i almost started being annoyed at her for making me that angry!It was at that point i got a grip
Also make sure you find 'down time' with her when it doesn't matter what you do and you can just chill and enjoy each other and have fun.
Finally, sorry if this is obvious but most common cause of tantrums IMO is tiredness/hunger/thirst so make sure her blood sugar is kept even - regular small healthy snacks - i always have a low sugar cereal bar or oat biscuit or something handy.
Do you have a partner? what's their take on it if so?
Hope this helps, will think on and post again if anything else occurs.Good luck!