Oh sorry I missed this the other day. This is a difficult situation for me since I have my own issues with closeting and personally I do not feel it is a sustainable way to live without creating some unhealthy neurosis.
However, it is obviously a breech of the previous promise she made to then talk about it to all and sunder. I think a good question to ask is, why did she feel the need to tell so many people? Is she just one of those people who are incapable of keeping things quiet (and to be honest there are a lot of those types of people about, it is not necessarily malicious, it is just an aspect of their nature. My BFF is a little like that actually, I still tell her stuff but with the knowledge that my counsel is only time limited!
Or, is the pressure of the closet simply too much for her? Perhaps she is used to having the freedom to talk about her family to everyone she meets, or may be she feels like she needs more external support for this whole change of lifestyle and she is naturally gravitating towards those who she has more day to day contact with?
It sounds pretty callous and mean, but I do feel, for the sake of the mental health of all concerned AND the fact that it is not the most ideal way to live, that people who need to be closeted, should avoid new relationships with those not raised within the Polygamist culture.