What happened to Amir's mother in The Kite Runner?

Amir's mother, Sofia Akrami, died while giving birth to
Amir in 1963. Sofia was a successful professor of classic Farsi literature at the local
university in Kabul--"the descendant of a royal family," and the reason that Baba
referred to her as "my princess." She was considered one of the most beautiful women in
Kabul, and many people were surprised when Baba married her, since he "was not of royal
blood." Amir knows little about his mother, but he discovers a few unexpected facts upon
his return to Afghanistan when he converses with a beggar on the streets. The old man,
Dr. Rasul, had also been a professor, and he remembered Amir's
mother.

"Such
grace, such dignity, such a
tragedy."

They had shared a
piece of almond cake and tea with honey, and she was pregnant with Amir at the time,
"and all the more beautiful for it." She had told Rasul
that

' I'm so
afraid... Because I'm so profoundly happy... Happiness like this is frightening... They
only let you be this happy if they're preparing to take something from you.
'