I am presently going through the same thing with friend whom I really, really like; our dhs get along too. She has 3 kids; but the youngest is closest to dd's age (almost 4) and she is also quite the handful. My dd is a relatively "complaint" child I guess you would say. My friends is extremely "spirited". I also think my friend lacks a little bit in the discipline department when it comes to her kids they can really be kind of wild and it seems like mine is always getting hurt lately. I have limited contact a bit.
We put both of them in a mother's day out program, same day, time and class. Just recently this little girl has been totally bulllying mine. Luckily the teacher let us both know and intervenes and separates them. This teacher even tells me what a handful the other girl is almost every week; there are only 6-7 kids in her class; so she is good about keeping a watchful eye out.
For my dd I told her if so and so is mean to you; tell her you will not play with her. My friend has been made aware of the situation and I guess told her dd that if she cannot behave she will not be going anymore.
I had that dd and her sister (5) over last week and this bullying does not seem to happen so much at my house and on my watch. I feel awful; it is hard to be the mom with the child that is bullied; and it is hard to be the mom of the bully; though like I said I think I would be more strict I feel she is too lenient about some things.
Recently at ballet her dd just ran up and pushed mine in the chest for no reason and I did raise MY VOICE right away and told her "so and so" don't do that; that hurts!!!!!!!! then my friend intervened; I am not sure she saw the whole thing she might have been writing out a check and I am not sure how she felt about that but enough is enough, she did grab her kid and drag her back (she was not even in the lesson just kinda running wild) and did say "so- and so you are so small to be such a big bully".
Ugh sorry to hijack, this has been bothering me to no end and I am not sure what else to do either.