How do you reply?
Putting aside the matter of consoling your friend — he is looking for an answer, not consolation — there are lots of possible responses. Some are more common tropes than others. Consider:
1. “God called her home. It was her time.”
2. “It was the act of an evil man, and God was not involved at all.”
3. “It is all part of God’s plan.”
4. “There is no way for us to know.”
5. “Probably because of something you did. Or she did.”