May be you are right... it could be Najma.because we know from Dilshad's recollection of things when she found the Doll, that Rashid took Najma to buy a doll and whatever happened in the doll factory happened that day, and most probably while Najma was there. so it could be Najma. and Zoya was supposed to be at least 3 years old when her fire incident happened. ..and this child on the chair does look smaller than a 3 year old.
And if your observation is correct, the mystery thickens more... may be Zoya was there playing with Najma (could very well be the reason why they hit it off immediately when they met as adults) and Zoya's father may not be Maamu but someone like a business partner of Maamu who was killed by raziya and Maamu.😛