What's wrong with my wife ? [I Marriage]

My wife keeps having bad dreams about her ex husband's death. This month would have been their wedding anniversary they would have been married 8 years. They had a son who just turned 10. He died in a car crash 2 years ago she was with him for 11 years they were married for 6 years. They were 15 and 18 when they had their son he was 3 years younger than her she didn't care she was madly in love with him. Me and her recently had a baby last month. What's wrong with her ? Why does she have dreams about him ? How can I comfort her ?