Sounds like a lot of talking is in order.
I think you just really need to find out what their thoughts and desires are on it (she may not even want to pop out a baby or be a parent), and clearly state your own trepidations about it, but also keep in mind that her body and choice is her own. It doesn't sound like you want to decide for her, but it is important to remember that another person cannot dictate what a woman should do with her womb. I think your focus should be more on your husband. If you and he are done having children, perhaps he can have a vasectomy. But again, that's up to him.
And you all should discuss your feelings and thoughts should an accidental pregnancy occur. Of course, if that happens, it is her choice whether to terminate pregnancy or not.
Maybe the thing to do is for everyone to agree that they are not to fluid bond. Wouldn't be such a bad thing for him to always keep it wrapped just with her.