There is a lot of point talking to someone about the assault you suffered. I think you should make it a priority to find out where you could go to talk about this. Rape Crisis? Individual counselling? Birth trauma site
You can also go and talk about the childbirth experience and bring up something that is not necessarily going to be in the notes. In cases of birth trauma the notes are not going to show the feelings of the mother or how she experienced the medical procedures or how communication between the medical team and the woman was managed, and not an assault. Going over your experience afterwards with the professionals who were there is about communicating your perceptions as opposed to what your notes say.
When you get a GP, please ask for a referral. You need to talk about the effects of the assault on you and not the baby.
After a horrible experience like that it is very understandable that you do not want to suffer any form of coercion wrt delivery or medical care. Even a straightforward delivery can shatter a woman's confidence in the medical profession, and your experience seems to have been a far cry from straightforward.
If you turn out to be positive for GD you are going to have to resolve the issues you have about fear of autism and also reluctance to deliver in a hospital environment and your problem with any form of perceived coercion when it comes to pregnancy and delivery. Even if you test negative, getting help in the aftermath of the assault is vital just so that you can begin to put it behind you.
I think I can see how this GTT problem is surrounded by other problems and also how it is such a sticking block for you.
Balancing risk involves knowing the risk. I think you are trying to avoid the definitive yes or no that the GTT would give you because of the issues you are dealing with regarding the prospect of hospital delivery. You need to know the risk. You need to weigh the pros and cons of hospital delivery with all the information to hand, including whether you have GD. You need to know the reality (GD or not GD) and from there you can assess the risks for you and for the baby.
I also think that without knowing about the assault the medical team are going to think you are being cavalier about the health of the baby, refusing to alter your diet for the sake of the baby, and opposed to medical or hospital intervention because of fears about autism that they will discount.
I think they will see your agreeing to blood pressure monitoring, home blood sugar monitoring, etc as you agreeing to things with your fingers crossed behind your back, and they will suspect that you will falsify blood sugar readings since they will result in a definite medical plan that involves hospital delivery, perhaps induction. To the medical team you will look like someone who is ignoring a real risk in order to have the delivery you have set your heart on or because you have a layman's understanding of research about autism or because you are anti-hospital.
Please be open with them about everything you are concerned about that is highly personal to you, and do not get involved with them in any debate about autism, research you have read, medical issues, etc. I think the real issues here revolve around your traumatic experience and you need to get help in having that resolved or at least acknowledged by the medical team when trying to make plans for your delivery.