Here's my $1.00/50:
My grandfather gave my grandmother a plaque which she hung in her kitchen for as long as I knew them. It said, "I don't love you because I need you, I need you because I love you." They were married for 65 years. Probably not because of the plaque but still, it was cool!
As a kid, it took a lot of thought to wrap my brain around that quote. Now, after 17 years of marriage, I finally understand it. I used to think I understood it after 16 years of marriage but NOW I can finally say I understand.
Bottom line is that you may find you're not going to be able to influence her at all in regard to her choice of a mate. I'm only 40 but in that time, I've discovered that no matter how much I care about someone, I can't change their minds and I can't live their lives for them. Once in a great while, I'll see someone about to make a mistake and I'll make a comment but it almost never has any effect. Never has. I doubt it ever will. The reasons are far too complex to go into here.
You've probably said your piece to her by now. It's probably time to sit back and let the chips fall where they may. The question you need to ask yourself now, however, is this: "Am I going to be there as a friend if things go south on her?" You probably already believe they will but how are you going to let it affect your friendship in the long run if it does?
I like the verses Thrasherfox posted but bear in mind, they are meant to stimulate thought and reflection. A great starting point. Hopefully, your friend will begin to think more critically of her relationship and will begin to see it more clearly, just as you wish for her to do.
One last thought I have before I stop preaching and rambling,
, if she's expressing concerns to you instead working them out with her future mate, it's a very good chance that her relationship with him is doomed before it starts. The right thing for a spouse to do in any situation is work out their difficulties with their spouse. Not a friend, not another confidante. Their spouse. If counselling is needed, they should get professional help and that is what your friend and her fiancee need at this point. They need professional pre-marital counselling.
As a matter of fact, I believe all couples should go for a little before getting married. At the very least, talk to a minister or someone who can give them a pre-marital checklist to talk about.
I hope she does well in any case. I hope you can accept her decisions in the end and still hope for her well-being in the long run.
Frankly, the one I'm worried the most about in this scenario is you. Tread carefully, bro.
--Wag--