I understand the memories seeing the knife can potentially bring up, but I would say try to talk to her and help her to realize that, like a gun, a knife is a tool. The knife cant rape, or kill, or harm unless someone uses it to accomplish those actions. Its like someone being afraid of a gun because they were robbed by someone with a gun, the gun didnt rob them, the person did. I would ask her if she would be open to sitting down and talking about it to make her feel comfortable, let her know the knife is just a tool and it only does what you want it to do because you control the knife. Dont force her to hold it or use it, but just talk to her about the knife, if you have a good relationship with her it may help talking with her to get her to accept a knife as just a tool and she may react better and more accepting to seeing one.
I can understand why seeing a knife traumatizes her because of the circumstances...does she react the same to something like a steak knife while shes eating? What I mean is does she panic around all knives or just pocket knives?
I hope I didnt come across as harsh...if it was one of my close friends, its probably the steps I would take...sitting them down and trying to talk to them.