*hug* I anticipate similar reactions from my own mother; I intend to come out to her this weekend. It has gotten to the point where I have avoided talking to her because of my fear that she can't accept the real me.
Here's where I feel I may be able to help a little... I'm also a parent. I have three beautiful girls (two step daughters and one biological). I met the two step daughters when they were five and six, I am the only father they have ever known. I will be coming out to them, too, as soon as I have an opportunity (I want to tell them face to face and it is a little hard to nail them down).
Anyway, my mother and I have been through some pretty horrific things together, including the death by murder of my father at the hands of my adopted brother, who, it turns out, was a paranoid schizophrenic at the time. I know a bit about grief, and about how it applies to your situation.
While a number of researchers have a problem with the model, the "5 stages of grief" are actually a pretty helpful system for understanding what we go through when we do grieve:
Denial - This can't be happening, that's my "son". It must be a phase.
Anger - My "son" had better not be doing this to me!
Bargaining - Maybe if I listen to "him" more, I can stop this.
Depression - Finally beginning to accept that nothing she can do will change your mind
Acceptance - Well, at least she's still alive and healthy...
These are all, by nature, selfish reactions... she is likely in enough shock and pain right now to not even be able to think of you, only what is happening to her as a result. That's perfectly normal... and you are *NOT* to blame. You are expressing yourself as an individual, and you are giving her the chance to know the real you. It's not going to be easy, but you have gotten through it, and she can too. *hug*
She will likely say more hurtful things... right now, she will be focused on getting you to give up on what is, to her, a crazy and dangerous thing to do. What she doesn't see and probably can't understand yet is that you are in greater danger if you do not do it. If a therapist agrees you need to transition, that is likely the reason why. It has been proven that things do not get better over time, without transition things generally get worse and worse. Over time, she will probably heal enough, accept enough to listen to that. Then she will probably begin to understand.
As parents are hard-wired to protect our young. If we see them doing something we perceive as dangerous we will do anything we can to stop it (or, if our kids are grown and we want them to be independent, we will try to calmly dispense advice, then shut our mouths and sit on our hands to avoid interfering, which is *much* more difficult to do... trust me on this!)
She can't ground you or otherwise punish you to change what she sees as bad behavior, so all she has are threats. When she sees that these aren't working she will likely begin progressing through her grief and will meet you on the other side.
This is not an easy road we are on, Izzy... not for us or for the people who walk beside us. But it promises a life fulfilled... and, really, when parents can step back from a situation and really think about it instead of reacting, that's what we really want for our children.
*hug* Hang tight, the storm looks pretty bad now, but the sky is clearing up on the horizon. And rain makes the flowers grow.