I am transgender M2F, so I have an understanding of your daughter’s situation. Gender Dysphoria comes with a whole load of shame, guilt, fear, depression and anxiety usually (I’m no doc however), so the fact that she’s opened up to you about this is fantastic. You reaching out for help and understanding is equally fantastic. I only wish some of my friends and family are like you!
This may be a very difficult time for you both, so please try to maintain the home-life as calm as possible – you’ll both need a safe place to retreat to at the end of the day. This road will be long, slow and painful at times. It can go for many years before a transgender person reaches their end-point (and that point varies from person to person) and feels comfortable in their own skin at last.
My road has probably years yet, and so will your daughter probably. Depression, shame, self-hate and guilt has been with me for years, but have faded as I became aware of my true gender identity and began a process of mental health treatment, counselling and medical (hormonal) treatment. I still have bad days, but they’re fewer and less intense now.
I wish you both all the lucj and love I the world – please let us know how things go if you feel like sharing.