The last paragraph in your post has the only feasible answer to your dilemma. All you can do is exactly what you have been doing, pointing out to her the pros and cons of her choices.
She is in a difficult position indeed.
There are quite a number of cultures were arranged marriages are the norm. Some cultures have a more flexible attitude towards a child not following with traditions and parental expectations on this matter. As you do not mention her actual origin, it is impossible to determine whether down the road there would be any forgiveness for her "disobedience". Anyone who suggests that mother and daughter can eventually mend the rift, is simply speaking from our own western, American perspective. In some cultures, she could lose communication with her parents forever, as she might be considered by them as having died.
Culture is a potent component in a person's psyche. Although growing up in the US many young people initially abandon their parents' ways, once they hit middle age they start reverting to the formation they received as children. At that point, many decisions made earlier on in life come to be regretted. Your young friend hasn't reached that stage in her life yet, but she stands a good probability of getting there. If the marriage should not work out for whatever reason, she has alienated her family and will feel immense regret. On the other hand, if she marries someone whom she does not love, she will be very miserable, especially since being surrounded by people of American/western ideas, she will have very little if any otside support for having done things her parent's way.
She needs more time. Even seemingly impossible things can change with time, perhaps even her parents. If her parents are not staunch, they might eventually come to accept that she will do things her way, or, she may herself come to realize something different about what she wants to do.
Another very risky but possible option would be for her to talk with the parents of the man her parents intend for her to marry and tell them the truth. This may create a terrible uproar, but at least then his parents will oppose their son marrying someone whom they will consider unreliable and scandalous. Just a thought....
The best thing you can do is to continue to let her know that you will be there for her no mater what she decides. The fact is that although you can not understand or share in the dictums of her culture, love is a universal language, and one that she is going to need to be spoken to in the near future, no matter what she does.
There's a lot of great Indian movies on this very subject, LOL