How would you punish marina for being a bully? Her home life is terrible and she's pretty young, so I don't think you can be too hard on her.
Personally, I'd bend her over my lap and give her a good spanking. Of course, I don't want to hurt her badly and I'd show her lots of love afterwards in a variety of different ways - but it's important to be stern and let her know that bullying is not tolerated.