Why would you lose her as a friend? Some people want to get married, some people want to have kids, and some people don't want either. But maybe you would change your mind. If she doesn't want to be your friend, that's her lose.
But I think you should compromise. Make her understand that at CURRENT PRESENT time you do not want to get married. The responsibilities, obligations and the financial stress is just too much for you to have to worry about now. But as time goes by, and your relationship with her becomes more serious, you'll give it more consideration.
Once you two move in together, you will have a better view of what it's like being married to her. But until then, she should just love you for who you are. After all, being married doesn't make you hers for life; it just makes it an expensive break up!
I once asked a friend of mine why he doesn't get married to her his girlfriend, his reply was "because I can't afford the divorce".