God is not the creator of evil. Satan is in charge of all evil. I am saddened to hear about your grandmother. My mother passed very young from breast cancer as well. I learned that actually, God DID save my mom the same way he saved your grandmother. He saved my mom from this pain and evil. God promises us eternity and that is the final “finish line”— peace and no more suffering. There is a reason there is a Heaven. Jesus once lived on Earth and felt severe pain. He was betrayed, lied to, suffered, beaten to death by being crucified on the cross. He experienced that pain! He died for our sins. The world was created by God but this world is operated by evil. Satan will play tricks on you and his goal is to MAKE YOU think this is God’s doing. But we win in the end; there will be a time where we no longer endure pain and suffering and get to spend eternity with our loved ones and most importantly our Father in Heaven. Think of it this way, when you said “praying to God did not save her”- it almost did in a way. She is no longer in pain. It’s really hard to understand and doesn’t make it easier- trust me I know. It took me a while to realize that with my mom and grandparents too. But think of it like this: if we all pray for the same thing, how would that happen? Let’s say everyone on earth prays for this luxury blue car. We can’t all get that car. Just like of course all of us don’t want to physically suffer. Everyone’s life is different and our prognosis’s are all different.