Transference is what pops into my head but hopefully more knowledgable heads will prevail. I find it interesting how you word it. She was cutting, claimed to be schizophrenic, went lesbian, etc, and now that she is transgender... that's when you draw the line. It's just interesting.
I've had friends and one longterm lover who were transgender, with a few gender dysphoria issues myself, and I can tell you truly that seven months isn't enough time to make a life decision like that unless it's something you have been thinking about for a long time but never have dared to talk about. Gender dysphoria is a VERY serious matter and extremely difficult to live with, treated or untreated. The feeling of living in the wrong body is absolutely horrendous. Usually you know it if you have it. It's important to be sure though and difficult to tell with a case like this, when someone might just think gender dysphoria is something you can just 'pick up.' It's not..
There are a few signs that can be seen in childhood, but some people get indoctrinated into behaving in hypermasculine (for boys) or hyperfemininne (for girls) ways. Many people are so threatened by someone who wants to change thier sex that it can be quite dangerous for the person. Death threats, rapes, and beatings are common for many transfolk. It is not a decision that is made, usually, but rather a deep need and a realization that you are not living in the way you were meant to be. What happens to a little girl who always wanted to grow up and be a father? Or a little boy who loves to cook and sew and is gentle, but everybody tells him he has to be tough? When inside he really feels like a little girl? There actually is a difference in brain structure, it's not just behavioral.
Sorry for writing a novel here but there is so much to say and so much important information that most people just don't have access to. If you have questions or if something didn't make sense, let me know. I'm happy to share.
Your friend may be trying to get attention, or have some other issues, but if she really is dypshoric then you should be kind and as understanding as you know how to be. If she turns out to be serious and really does have this issue, please respect her decision. You may be saving a life.