Well I dont really have this problem being that I am close with both my sister in law and mother in law but I can try and help as much as possible. She obviously is lacking something in her own life by medling in others so take that into consideration. Maybe she is envious of you cause she was really close with her brother. Maybe she just likes you. But I know the kind of person you are talking about. I use to have a copycat too. Buy something that she hates and go someplace she wouldn't be caught dead in. See if she really is all that copycatish. I honestly would take it as a compliment but if she is driving you insane, then, maybe you should just ignore her. I know that sounds more difficult than it really is but ignore her. And if she starts mentioning that you are ignoring her, tell her you had no time to deal with those problems. You have kids or a family of your own to maintain and not her 24 year old antics. That's what I would do. Hope it helped.