9year old girls behaviour (updated)

Hi, I will give a full account with as much information as possible to get some advice and support.

I have a 9year old daughter who has always been a well behaved child she had a few tantrums when under 5 but generally good. Always good around others and tantrums were always towards me. I was a single parent for 4years. In the last 5years she has adapted to bringing my current boyfriend into her life and they have a good relationship. He spends time with her and they enjoy days out etc. We are now expecting a baby in September. My daughter over the past 6 weeks has become more angry and shouting at me more regularly. She will say no firmly and consistently then scream and shout if we have to so something she doesn't wish to do,this can be having a shower, picking someone up, walking to a shop or family members. We have taken away her kindle when she has these angry outbursts and she will do anything to get it back, we have a good few days with a few reminders of behaviour and then she outbursts again. We have ensured we give warnings of when things are happening so it's not a sudden order. She can't handle choices or make decisions either.

Is this because of new baby and her fears of how much time with us she will get or could it be hormonal or does anyone have any other suggestions.

My daughter is now 10 and has a 10week old baby brother we have had ups and downs and her struggles are now slipping into her school life. She is showing lots if signs of pathological demandavoidance and we have the school and gp on bored in finding support for her.