Well they are at 2 different ages developmentally.
So their cognition is different.
I have a daughter and son. My son is the younger one. They are 4 years apart.
But for the most part, they get along and like each other.
Sure they fight sometimes, but they mostly like each other.
I think, siblings either get along and/or like each other, or they don't.
Me and a sibling I have, never got along. We were like oil and water.
But yes, you do need to guide/teach them/discipline them. Because, hitting is wrong. But per the 2 year old's age, they do this. But so you have to use different age appropriate methods, to correct them.
Tell your daughter, to talk in a normal voice.
Separate them.
TEACH them, and you, that siblings can have alone time too. And they may want to play by themselves too. This is normal. No siblings, HAS TO be playing together ALL the time. I taught my kids, how to NICELY say.... to me or to each other, if they want alone time or to play by themselves. And its okay.
If your daughter is always feeling, that her younger brother always trumps her, then well, she is acting out because of it.
You need to talk to her, teach her how to say things in a NORMAL voice, because screaming about it does not help. And that you will hear, her.. even if she is grumpy or sad. That she needs to tell, you. And that, you know she is just a little kid, herself.
2 year olds, do not have full impulse control.
But still, he needs to be corrected.