I have two children who are very similar in age to yours. Whether or not the older child is going to listen to you depends on what kind of structure you have set up for her in regards to discipline up to this point. If she's been allowed to just do whatever she wants then suddenly trying to get her to behave is going to be rough sledding. That being said, if you want her to stop yelling at her brother, then every time she does it, there are going to have to be consequences, like a time out, for instance. It's exhausting.
Does she like playing with him? If so, then the punishment should be that she doesn't get to play with him.
And then, some kids are just tough to manage and very little seems to work. Ultimately, I think, the more structured you are in your response and the more consistent in your response, the more likely you are to be successful.