Bp. Sanborn wrote recently in one of his newsletters that a lot of transgender children have high rates of ѕυιcιdє and depression. He gave an interesting theory as to why this is so, and you may find this helpful. He said children now are being put through these Frankensein-like transformations before the reach puberty, i.e. before they understand the decision they are making. Then, when they reach puberty, they understand the proper relationship between the sexes, and they want to have a normal relationship. But what can they do? Who can they marry? Someone of the same (original) sex? Someone of their "new" sex? Neither one really works, and they realize they are stuck and have to go through life without a normal "relationship" to use a somewhat worldly term.
I don't know if the person you are talking about is an adult or not, but maybe explain this to her. Who is she going to spend her life with? A (real) man? A man is not interested in a woman who has changed her body into a "man". A woman? A woman is going to want a man, and a real man, not a woman who has turned herself into a fake "man". Another transgender person? Of what kind? There is no way any of this works.