I think that for everything there is a season. If this woman were suddenly faced with the loss of her sisterwife would she go on a quest to find a replacement? Or would she take time to mourn the loss of her loved one and then gradually start thinking about the idea of a new person.
My point is that while she may feel that being a sisterwife is a necessity, if one of the wives were to pass away, wouldn't you want to observe a period of mourning for her? Or would you rush right out to find another?
My feelings on the matter are that as with any other relationship, there is a mourning time at the end of a relationship. A time when the remaining parts of the family feel free to mourn the loss of their partner. When they can cry anytime they want to because that person is no longer a part of their life.
Mourning takes different amounts of time for different people. If my sisterwife dies, do I automatically have to start finding a new sisterwife as soon as she is buried? Or can I be like any woman who loses a spouse? And take time to adjust to life without my sister in it? When my mother dies, I don't plan to go find a new one? Same with my father.
Just a thought. Even in polygamy there needs to be time for people to grieve and mourn their losses.
SweetLissa