God has put within each of us a strong desire to keep on living, and it's not necessarily wrong for us to want to take care of ourselves and keep death at bay. The Bible says, "Now choose life, so that you and your children may live" (Deuteronomy 30:19).
The Bible also tells us that death was not part of God's original plan for His creation; it came about only because of sin. In fact, the Bible labels death as our final enemy that will only be destroyed at the end of time (see 1 Corinthians 15:26). We mustn't take death lightly; not only does it bring our life on earth to an end, but it also marks our entrance into eternity -- either in that place of absolute hopelessness the Bible calls hell, or in the joy of heaven with God forever.
But the good news of the Gospel is that Jesus Christ has conquered death! By His death and resurrection He overcame the power of death and opened heaven's doors for all who repent of their sins and turn to Him in faith and trust for their salvation. Think of it: Because of Christ, we don't need to fear death any longer!
It's easy to become overly preoccupied with our health -- particularly as we grow older. But when we know Christ, we know that someday we will go to be with Him forever -- and that makes all the difference. Pray for your aunt, and encourage her to take time every day to thank God for Jesus' promise: "Because I live, you also will live" (John 14:19).