You have most likely already spoken to her and/or her dominant about what her limits are, but more importantly than that I would speak to her and/or her dominant- perhaps even just her dominant- to find out what she gets particularly excited about and incorporate that as part of the scene. As the other reply suggested though, keep it to yourself. Don't let her know the details, and certainly don't let her know that you plan on doing something you know she will be especially turned on by.

I have had experiences with submissives who enjoy humiliation/rape scenes and one of the favorite activities I enjoy while doing a scene like this is to use a blindfold and sound recording device. After she is blindfolded, make her walk, or crawl , into another room. Tell her she is on a stage, tell her she is going to be on display- you get the idea. Then play back recordings of background conversations to give the illusion of other people in the room so you get the illusion of a room full of people watching when it is only you and your wife and the "victim". A good source of these background conversations, if you don't want to make your own, is to just use your recording device when you go out to dinner and record normal dinner talk and then adjust the replay so that it is not quite clear what is being said.

Good luck.

Drake.