I work with children with behaviour difficulties. So i will tell you the practice that we use.
Pick on the one behaviour you want to work on at that time. Don't pick all of them at once or you will go nuts and feel like that you are getting at her all the time.
I'm not sure of how you reward and reinforce good behaviour?
What we do is reward the child who is doing the right thing. For example: Brother is sitting nicely doing what you are asking, sister is playing up, he gets the sticker. You say to him, "well done * you are doing the right thing, you can have a sticker". So many stickers and the child gets a treat. She will hate this as she is not getting attention so if she plays up and he is not reacting to it he gets another sticker. etc etc.
She will learn that bad behaviour will not get rewarded. This is hard at first and she may play up more until she realises.
We use what we call BODORS : blatantly obvious dose of reality speech. Which are clear instructions.
eg
you need to .......
the instruction was.........
the adults are in charge........
that is a personal comment you need to keep that in your head
(you will need to explain that just because it's in your head it doesn't mean it has to come out of the mouth)
Don't get drawn into a conversation with her, this will give her the attention she is looking for. At five they have a short attention span and will switch off.
Label the behaviour not the child. Don't use "you" but, "snatching that toy was the wrong thing to do".
Don't take things away, it will end up that she has nothing to work for. I made that mistake with one of my children. Instead give the brother something extra for doing the right thing.
Remember to keep a calm constant voice, she is looking for a reaction.
If she needs a "time out" that's fine. But the time out only starts when she is calm. It's no good doing a minute on the stairs for example when she is angry, she will still be angry at the end of that minute. One way is to teach her to put her hand on her heart and feel her heartbeat, the difference or angry and calm. Once she gets used to the idea of "time out", you can give her the choice and ask her if she needs a time out before she blows.
We always make the children "put things right" to say sorry for what they have done. We never say, " that's ok" because it's like saying the bahaviour is ok. We just say "thank you".
I hope this helps