So, her partner sacrificed for his country and has suffered for it, and her response is to lie to him and betray him. And you want her to be a part of your intimate lives why? You trust her why?
My advice would be to tell her that her options are 1) break up with him, 2) come clean and work things out with him such that she can continue to be with you guys ethically and honestly, or 3) stop seeing you guys. He deserves honesty, she deserves a clear conscience, and you and your wife deserve to be with people who have integrity.
All of that aside, why do you want her to be exclusive with you at all? Why not enjoy her company and let the relationship evolve organically while leaving her her freedom? There is a lot of complex stuff going on in a three-person entanglement, especially when two of the partners have been together much longer, and the sort of model that you seem to be aiming for rarely goes well -- do a tag search for "unicorn hunters" if you want to see some examples of the sorts of problems that tend to arise. This essay may also be a really useful resource as you think about how this relationship, if it does indeed continue, might evolve -- http://www.morethantwo.com/coupledating.html