Have you told her that you would enjoy seeing her being with another woman? It may be that she is afraid you would "join" in and want to be with someone else more than be with her. If she knows that "you" just want to watch and perhaps masturbate she may be more inclined. It may be that she is just embarrassed as well. It may be better if you explain if she wants to fulfill this fantasy you are for it. You could post something on an on line swingers ad or look for someone and allow her to just be involved by herself to begin with and then may be after a time or two, you could watch.. or you could watch by peaking in rather than be in the room fully. Give several options how this could happen and then just tell her to think about it for a couple of weeks and then let you know when she is ready to talk about it.. Assure her you would love this... to happen and it wouldn't hurt your marriage in the aspect of not loving her..

So basically by doing the above, you plant the see.. it's then up to her to allow it to either grow or not to grow.

Hope this helps Hun, if you need anything else please feel free to ask.