My heart breaks for you - of course you want to know why this happened and why God allowed it. If it were me, or one of children experiencing the same thing, I would want answers too. When you love someone, you become vulnerable to the sorrow that comes from losing that person.
Shock and grief are devastating emotions for the human heart to endure. They shake us to the core. Yet in the midst of that sorrow and pain, God promises to be there with us. It will take time for you to find a way to cope, and that can best be done by allowing others to surround you with support and understanding. Let others help you grieve. Let others listen to your thoughts and feelings. Let others hold you while you cry.
Over time you may begin to see how God can use this experience to draw you closer to Him. God works that way - He knows what is in your heart and the sadness that consumes you. He is the only One who can help you move forward with a new set of eyes. Only He can turn your sorrow into something meaningful. Please be patient.
Let God carry you for now. He is your Great Shepherd and can comfort you when you need it the most. He lost a loved one too, so He felt loss much the same way you do.
Can I pray with you?
"Lord, I pray for my friend here who is grieving and trying to cope with this overwhelming sorrow. I pray you will wrap your love around her so tightly that she will know without a doubt that your love is greater than any other force on this earth. I pray you will calm her heart, and put her on a path that brings her closer to you. Amen."