Dear K.,
It sounds like you 3 year old is actually responding to the changes in her life. She is unhappy about the separation and is acting out to get attention and control something in her life. She can't control most everything else, but she can control you through her actions. My best advice is to get her and your whole family in to counseling quick. Being able to talk about things will be of some help. Secondly, be firm with her - loving but firm. Establish rules and don't back down. Don't try to be her friend, you are her Mom . As much as it hurts, you will have to take a hard line if you are going to get anywhere with your 3yo. Set ground rules and if she crosses them, give firm consequences. Next work on a positive chart that rewards good behavior. If you want her to use the potty, give her a sticker each time she does. Tell her if she goes all day on the potty without accidents, she gets something she wants. Remember, most of all she needs to be assured of your love and commitment from her. She is testing you to see how far she can go. Don't let control you with bad behavior. If she screams, send her to her room. Close the door and keep her there until she calms down. If she is violent with you or her sibblings, give sever consequences. If you let her get away with it, she will increase the negative behavior. She really wants to see what you will do. Good luck to you. I know this is not easy but if you are strong in your convictions, you and she will get through it. Take care, G.