Your cousin has probably asked the same question you have, and I'm sure her path has not been easy. But in the midst of it all she has made a very important discovery: God is with us even in the midst of life's hardest situations.
In other words, the reason your cousin feels this way is because her faith is stronger than her circumstances. Many people, frankly, fall apart when life turns against them—and the reason is because their faith was weak to begin with. They are like the man in Jesus' parable who built his house on sand; when the storms of life come they are washed away because they have no solid foundation of faith in Christ (see Matthew 7:24-27).
But long before this accident happened to your cousin, she gave her life to Christ (as your letter says elsewhere). And she not only committed her life to Christ, but she grew strong in her faith through fellowship with other believers, and through prayer and reading the Bible. She is like the other man in Jesus' parable: "The rain came down, the streams rose, and the winds blew and beat against the house; yet it did not fall, because it had its foundation on the rock" (Matthew 7:25).
What about you? How strong is your faith? Don't wait for life's storms to assail you, but open your heart to Christ today.