I don't see Shabnam as heartless at all, I see someone who was deeply traumatised by the circumstances surrounding her pregnancy and fear that her family/mosque would judge her. Before she left Albert Square she was a normal young woman and she's changed out of all recognition. To me that's evidence she went through something profoundly distressing.
We saw she cares about her daughter when she first confessed to Stacey. She feels deeply guilty for abandoning her which is why she became so much more devoutly religious. Also she gave her a name - something I don't think someone heartless would do.
(Shabnam's state of mind reinforces my long held theory that Dean raped Shabnam. If it's true it explains feeling dirty and ashamed, over and above her religion and fear of her parents' disapproval. I still haven't completely given up on this theory despite her denying it was rape. She could have repressed the memories because she couldn't cope with them.)
As for Dean making a better father, I have to strongly disagree!!! I believe Shabnam's good at heart and, if she ever makes peace with herself and gets the chance to be a mother to Roya, will make a decent job of it. I'd never say the same for Dean, who's only capable of caring for himself in my opinion.