Boundaries are not just important, they are essential. I'll tell you why...
The first step to being a supporter, a good supporter, is first looking after yourself. I can see from what you have written since the beginning of this thread that you aren't looking after yourself, but you are crying out for help. So help yourself first. You cannot support her if you yourself are screwed up.
Set boundaries with her when she is having a good-ish day and she can remember what is being discussed. PTSD and its symptoms are one thing, but abuse is another. You cannot allow her to do things, things that you would not stand for were she well. So tell her what hurts you, what you consider intolerable, and get her to agree not to do them.
Then when she does have a bad day, and she does do them (and she will) then you decide what you will do. I usually retreated and gave her her space to figure it out, these days I let her know straight out that what she is doing is not allowed, screw the eggshells. She actually seems to somehow appreciate the honesty and directness that I show in ths regard. Someone else might take it differently.
Refuse to accept, or take her abuse. When she sees that she still needs to behave in a civil, acceptable manner even when she is freaking out, she will probably find comfort in those boundaries, and start sticking to them.
Well, this is how I deal with my sufferer, and after 6 months of marriage to her (tomorrow!!!) it seems to be working well.
Oh, and if you are serious about your relationship, and you are committed to staying with her, then tell her that. Often, and with feeling. She seems to become quite insecure during an episode, and allaying her fears may go a long way to comforting her.
best of luck dayglo, its not going to be easy.