My baby only poops after wearing her new diaper and it became a habit for her. Any idea on why she does that?

I had the same problem. My son would not poop in the potty. Try getting her to sit on the potty with a diaper on. This gets them used to just sitting and pooping, even if it's in a diaper. So, tell her she can have a diaper, but she will have to sit on the potty. After you get her used to that, cut a hole in the diaper. Kids are smart, so don't let her see it. Put the diaper with the hole on and have her sit. Soon she will realize the poop is in the potty. I explained this to my son by telling him he was now too big for diapers or pull ups and that the poop was falling out. It might take a little practice, but it worked for us!