It appears that your mother has the problem in this situation. From what you have written, she seems to have only been involved in your younger years when it suited her.
Your main goal in life from now on, will be to focus on your transition/reassignment treatment - as that will be an emotional journey in itself.
You have the support of your father and your boyfriend. During this time of your life, their support will be beneficial to you and it's a positive situation knowing - in yourself - that you are finding your own true identity.
However. It is very important to recognise your PTSD diagnosis and the issues concerning your mother. Your transition journey will benefit from the support of your family, friends, work colleagues and - above all else - yourself.
PTSD in itself will create a challenge. It is important to undergo and continue regular counselling/therapy in order to explore and understand the issues of your life so far. This will also help you to deal with the emotional rollercoaster of your transition.
Although you know in yourself that this change in your life will enable you to realise and fulfill your true life's ambition, it is still a big change. Regular counselling will enable you to ensure your mental health stays in control whilst you undergo your transition.
One thing for certain. Your mother hasn't helped.
You say that your mother has been 'in and out' of your life. The questions....Especially now that you are older....Do you want your mother in your life?.....And....Does Mom want to be in your life?
All the good, positive work you have put into going through your transition and getting your life sorted out could be put in jeopardy because of your mother's behaviour. This will need to be addressed as soon as possible.
From what you have written, your mother appears to be at least one main reason for your PTSD.
Counselling will help you to deal with the condition and understand the trauma that your mother caused (or at least contributed).
Depending on how you feel about your mother being in your life, you will need to decide how far you want to go with it. For example. Do you tell her not to see you again? Do you cut her out of your life completely?
After what she has put you through, it will be understandable - as you don't need this in your life right now.
On the other hand. Your mother may have a weird way of showing it, but she may still want to be a part of your life. Even after all these years, she just can't seem to get it right.
Perhaps Mom wishes she could be a part of your life and can't express this.
Should your mother want to be an important role in your life - and make amends for her previous mistakes, then she will need to change her lifelong ways.
That's a decision for you both to work out together.
Your mother has behaved the way she has because of her own life issues. It appears that she has more than expressed her anger, frustration or whatever upon you.
If you and your mother are to have a positive adult relationship, then your mother will need to seek professional help in order to understand her own life journey. Your mother's behaviour towards you is unacceptable and the time has come for her to change her ways.
This will need to be a condition that will be the basis of her being a part - and sharing the rewards - of your life.
You have had to make important decisions that will shape your life in future years. You have the support of your boyfriend and father.
There may only be a slim chance. However. You could have the support of your mother if she will accept her past mistakes and make some important life changes herself.