God doesn't always answer our prayers the way we wish He would -- but He does answer them. He is never deaf to the prayers of His people! The Bible urges us to pray "on all occasions with all kinds of prayers and requests" (Ephesians 6:18).
Hard as it may be for you to accept right now, God did answer your prayer for your mother's healing -- because now she is in heaven, completely free from every pain and weakness she experienced in this life. One of the Bible's greatest promises is that some day we'll leave behind all the troubles and sorrows of this life. In heaven, the Bible says, "There will be no more death or mourning or crying or pain, for the old order of things has passed away" (Revelation 21:4).
This is true for your mother right now -- and some day it will be true for you if you know Christ. I know you miss her very much, and you wish she hadn't been taken from you. But in the midst of your sorrow, may you turn to Christ and find comfort in Him. God's promise is true: "Precious in the sight of the Lord is the death of his saints" (Psalm 116:15).
Remember: God knows what it is to experience sorrow -- for He endured the greatest sorrow the universe would ever know: the death of His Son. But by His death Christ won our salvation, and now we have hope -- hope for this life, and hope for eternity. Make Him the center of your life -- beginning today.