From your description, your friend has certainly not acted honorably in her personal life. But I don't see where she has acted badly towards you (indeed, please forgive me, but I see a lot of judgment in your posts - why did you need to mention that she portrayed her relationship with her husband as "so in love"?)
From an etiquette perspective, she is absolutely not obligated to share personal information on facebook, even if not sharing that info causes some confusion.
Relationships are complicated, and I frequently remind myself I don't know what goes on behind someone else's closed door. As a friend, I may feel entitled to information or to have my opinion listened to, but if the person does want to share or listen, so be it.
Not that I don't understand your frustration with the situation - I do. I just don't think there really is a means to address it.