She sounds very normal to me - I realise this is not what you want to hear, but she really does sound like a typical two year old.
She is not nasty, she is not a bully, she is not mean - she is going through a phase that almost all two year olds go through. Her behaviour isn't what you want it to be, but that doesn't mean she as a child is nasty. Two year olds think the world revolves around them - they all do. She has no concept of ownership, she isn't old enough to have developed any sense of empathy or compassion, she can't equate how she feels with how other people feel. All of this is normal - I know it feels insurmountable but it is a phase and it will pass.
Pick your battles, because you are too tired to continue like this. Let her have her own way sometimes - she needs to experience this in order to know how to handle it. Let the little things like who sits on which chair go - sit on a different chair, or have your bedtime story somewhere else where there is more room. It might be her who starts the fight, but it takes both of you to continue it. And she is still a baby, who doesn't really know how to handle her feelings.
I feel this is as much about your emotional state as hers, and it would be a shame to label her when it's not all about her.
I think it's also partly that there is a new baby coming. That alone will make her unsure of you and your love, and make her push the boundaries even more. She needs reassurance that you will still love her even when the baby comes - so she pushes for attention because she still wants to be your baby.
Be nice to yourself, be nice to her as well. It's hard, but you have to ease up on her a bit. And you have to stop thinking of her as nasty, mean and all these negative things - otherwise that's how she will see herself too.
Keep your chin up ... it will pass.