Well, not that it helps sort the mess out or help with the grieving, but you've just learned why honesty is so essential in relationships, in general, and poly relationships, in particular. Your wife wasn't honest about her experience and now it's upending three lives.
At this point, I don't see any way to save it. I certainly couldn't trust your wife to be honest about anything after this. If she's too distraught to care about anybody else's pain, she's likely to cut wounds into you and ElfChick that will take a long time to heal and likely preclude any possible strong ties with her, ever.
I can only hurt along with you, for I have no words at hand that I think can help.