Thanks for your message. It really sounds like your family has been through a lot, I’m so sorry you’ve had to bear so much trauma. And thank you for reaching out to a trans person for help in supporting your kid, who has been through so much.
I want to say, with compassion, that you are asking the wrong question. You will never, ever have a definitive answer of “why” your kid is trans, or where the dysphoria “came from”. Most people who experience dysphoria did not go through the things your child has gone through. Lots of people who do go through trauma similar to what your kid experienced do not end up trans. So it doesn’t really make sense to understand your kid’s identity through the lens of those experiences — you will truly never know if they were a factor.
You can’t ever go back in time and see how your kid would have ended up without those experiences. You will never have an alternate reality version of your child who did not go through those things. You will only ever have the child you have now. You have not “lost” a version of your kid who was younger and different — all children grow and change as they age. Happy kids sometimes become sad teenagers. And we all suffer and get more complicated as we age, too. That is a part of becoming a fully-formed adult, and it is as beautiful as it is hard. There is no going back.
So my answer to your question is this: it doesn’t matter where your kid’s trans identity came from. You’ll never know the answer to that. My questions for you are: What are you going to do now, to love and support the kid that you do have? What does your child want from you, in order to feel loved and supported? What is making life hard for this kid right now, and how can you help to make a little less hard for them? How can you work to believe and trust your child more, and listen to their needs more? Those are the questions you should seek answers for, in my opinion. Not the question of why your child is the way they are.
Your child has been through a lot, and being transgender in a transphobic world is another really difficult thing this kid is now facing. I wish you the best of luck in supporting them, loving them, listening to them, and accepting them as they are — trauma and dysphoria and all.