Hi M.,
Wow, you have your hands full! I know you cant be everywhere but I think the 3 year old is getting lost in the shuffle.
I am against biting, scratching, hitting or bribing the child. YOU are the parent and the child shouldnt be selecting a form of discipline.
She is getting a lot of negaitive attention by acting out against her brother. Nail polish, socks etc.the focus is on her hands and not the behavior of striking out at him.
Remove her from the situation and us a time out spot making her sit there for 3 minutes, telling her why she is there. Do not interact with her for 3 minutes except to return her to that spot if she moves away...it may take seven or more times until she knows you mean business. Be consistent evry time she scratches him.
At a totally unrelated time sit with your daughter. She is obviously angry. Talk with her and see if you can find out what's going on. If she doesnt feel protected this may be her only recourse.
I'm wondering what HIS part is in all of this. Is HE poking her behind your back or taunting her? Perhaps they need closer observation to see what is really going on.
CONSISTENCY with time out will work.
Its a tough job but its worth it. Perhaps they will obe day become best friends. It is our hope as Mom's.
Justine