Is Shazia/Nazia is Seher? The possibilities are right there...Tanveer can be considered evil, but she was taking revenge. I don't think she wanted to hurt the baby for no good reason. She might have even taken Seher as Asad's child.
Plus She has a inhaler, her lungs are damaged...could be from the smoke of the fire that supposedly burned the house down. Remember the officer who told Dilshad about a fire in the house and Dilshad fell down because it was the Ahmed/Gufoor House