Mariam is definitely capable of looking after herself. Except for her own mother trying to take care of her, who else has been there for her? Mariam has been forced to care for herself again and again in her life. Furthermore, even going beyond protecting herself during the beatings, she takes care of the other wife and the children, saving them all from her husband by killing him. This moment clearly shows her ability to not only take care of herself, but also her strength in taking charge of a situation of which she has clearly had enough.
Maram could take care of herself through the care and nurturing of her teacher, though she did not receive much in the ways of life from her mother. She ends up not only protecting herself, but others as well.
Mariam has had what little nurturing her mother knew and was able to give her, but she also had the guidance of her Koran teacher to help her draw from her own strength, understanding of justice and morality. Intellectually, Mariam was capable of making the proper choices to take care of herself and others. Emotionally, she was starving to be loved, protected and nurtured by her father, because she lacked it from her mother, then hoped she could recieve it from her husband. When it seemed hopeful that she could and joyous that she would with a baby coming it was that more desolate and painful when she lost it. To have loved and lost is painful, but to have never loved at all is agony.