When her friend is ready and is strong enough, my prayer is for her to focus that anger and desperation to a laser light sharpness so that her daughter battle and passing is not in apparent vain. As you said so eloquently, the question is this: was her daughter journey undertaken due to contaminants in the environment that may have activated a heretofore silent oncogene? Did it cause her body to begin fighting against itself in response to manmade carcinogens? Or was her body programmed from birth because of some mutation in her code or maybe is was something that was could have been prevented, because of a preprogrammed issue, ( if it known to medical science) with a supplement designed to prevent the development of the disease?
Everyone's life has a purpose, though it may seem so small and meaningless to us as a race. We need to look at each life through heaven's eyes. Trust me, I've been in the Lobby a couple of times, (I've had 4 NDE'S) and that's how they roll. This may be the opening shot in a life of a warrior who fights for the lives of other little girls and boys so that they never have to fight the battle her sweet little one did.
It's going to take a bit of time for her to arrive at the place where she can see things through Heaven's eyes and that's okay. God understands. She may leave the spiritual path she's been walking all her life and it may be that she's so hurt that she no longer finds comfort in God. Guess what? I don't believe in a God so cruel and heartless that he would damn someone who has been so hurt that she can no longer see the light that led her for so long. Right now, that isn't as important, (I can't believe I'm saying this so it must be coming from that mediumistic side of me)as your friend finding her feet once againGod is infinite and has infinite patience.
So, if she stays angry at God for the foreseeable future, that's alright. Just be there for her as a friend and someone to hold onto.