what can help nightmares

My wife keeps have nightmares in this dream she is reliving a trama that happen. To her up till she was nine years old. What or how can i help her? Is there anything i can do different. Then hold her and reassure her. The nightmares are happing alot more and she is not sleep alot because of the bad dream. My wife feel a shamed and week and i dont think she should feel like think. But nothing is help. We can’t find the. Trigger that is causing it. Please help if you can. Also she dose not like to talk about her past and has always been able to.