Tell her the brutal truth on how this affects you, if she accepts it and understands then you have nothing to worry about. If she does not understand well then only you can decide what to do from there.... I would suggest you sit her down and tell her everything but understand that she may have insecurities as well that she is not addressing or just ignoring. People deal with things differently, your fiance may just not see your hair loss as a issue as you do. Or she may feel cheated that you may be taking your (yours and hers) time and money to treat something that only "you" care about. She may be thinking that money or time would be better off to start a family, buy a home, a car... etc... You are about to embark on a journey, marriage, that means you are both married as one.
I hope you find your answer but the common theme here from all the members is the same, TRUTH...