Hello Morgan,
There are no easy words to say, you're in a Catch-22. You're damned if you do and damned if you don't. It sounds like your friend is in an abusive relationship. Somehow she has fallen under the control of the fiance and nothing you say or do can shake that. Part of what an abuser does is isolate the victim from all their friends and family. They become emotionally and financially dependent on the abuser and see no way out. If the physical abuse has not started yet, it will.
If you love your BFF you've got to do one of the hardest things you've ever done -- be there as a safety net. Not only that, but you've got to realize your friend may actually end up abandoning you for some reason. You may not hear from her for months or perhaps years. This is part of the abusers attempt to isolate her. It will also be her way appeasing him. She will fear being hit more than the need to be in touch with you.
So what should you do? I'd stand up for my friend. Right now, the wedding is still about a year away. A lot can happen in that time. Use that time to talk to your friend. She knows you are worrying about her but that does not seem to be getting through to her. Does she want children? If so, if the fiance is abusing her, he will abuse the kids. Does she want that for her children? If she doesn't care about herself, she should care about her kids. If the dad abuses the kids, they will come to the attention of the State Protection agencies. If it is bad enough the kids will be taken from her and placed in foster care. Does she want that? Or worse, the death of one of her children?
Your friend needs professional help. You can let her know you are there for her. You can try calling the closest women's shelter and speak to the staff. Perhaps you can get your friend to the shelter to show her there is help available for if and when she decides to leave this relationship. Just remember you can lead a horse to water but you can't make it drink.
In the end, your friend is making her own choices. Be careful she does not drag you down or into a situation where you get hurt. If drugs are involved, you could be charged with a crime just for having them in your car. Your first responsibility is to yourself, your family and your life. Despite our best efforts, there will always be people beyond our help. Mourn the lose and move on.
I wish you all the best.
Howard Kier, Certified Professional Wedding Photographer
Magical Moments Photography