Sanuabar is Ali's wife and Hassan's mother. Aside from her beauty, she is the polar opposite of Amir's late mother, Sofia Akrami. While Amir's mother was of royal heritage, a university professor of Farsi literature,
... and one of Kabul's most respected, beautiful, and virtuous ladies...
Sanuabar had apparently prostituted herself before (and possibly during) her marriage to her cousin, Ali. Amir relates the story of Hassan being accosted by a group of soldiers who claim to have had sex with Sanuabar. Shortly after Hassan's birth, Sanuabar
... ran off with a clan of traveling singers and dancers.
Amir discovers much later in the novel that Baba had actually impregnated Sanuabar (Ali was sterile) and that Hassan was actually his own half-brother. So, while Amir's mother was of royal lineage and died while giving birth to Amir, Sanuabar was a tramp who gave bore her son outside of marriage and then soon deserted her Hassan.
Sanaubar is Hassan’s mother and was Ali’s wife before she left with performing travelers. She abandons Hassan after he is born and is considered immoral in her younger years but she becomes a caring grandmother to Sohrab later on.
Amir’s mother Sofia Akrami is not seen in the novel as she dies when giving birth to Amir. Amir believes his mother to have liked literature just like he does although his father would prefer he participate more in manly activities.
While Sanaubar is considered immoral, Sofia Akrami is considered to have a strong moral sense. Sanubar is from the Hazara ethnic group which is marginalized and considered second class by the Pashtun, a dominant Pakistani ethnic group while Amir’s mother is from a royal Pashtun bloodline.