P.R.
All you can do is really keep a positive attitude. When she starts in tell her she can only say positive things. When she starts to push a button tell her she has to take five minutes and say something nice about everyone in the room. If she doesn't want to it is fine but she will have to go draw and color a picture of something beautiful. Ask her to help you do something nice for someone. This can be helping pick up the toys, set out a snack, whatever. If the other children don't want to play with her don't force the issue. She is old enough to understand a lot more than we realize she does. Explain to her the other children want to be happy and you want her to be happy but if she doesn't do and say nice things she will have to spend a lot of time alone. If you make it a policy they can not say negative things while they are in your home or play alone they will all get along better.