One thing that is reiterated in many of the books and dialogue exploring polyamory, and should be common knowledge for any relationship, is if you don't solve the 'problem' no amount of adaptation and/or exploring will cure your issues. If the person in question wants to 'cheat' then there may be a problem that needs to be addressed in the relationship beyond possibly wanting to be polyamorous, especially, since she has yet to even attempt to discuss it. I mean, there may not be a problem but, if not, it would make me curious as to what's the issue with asking? I, also, believe it is her responsibllity to initiate this conversation with her husband not yours because it has to be her desire and, ultimately, it is their relationship that has to try to re-mold itself into what they want. It also makes it difficult when there is someone already waiting in the wings. That's unfair to the uninvolved partner because it gives the impression that they have to make a decision 'now' instead of being granted as much time as they need to ponder this idea and this change and accept or deny it. So...those are all some things to reflect on. I hope it all works out for you.