It does get a bit tricky sometimes. I cannot say I am always 100% aware, but that is, in large part because I don't feel I get a lot of feed back.
I try hard to do 2 things in general. I think of them as acknowledgment and checking in.
I do try to acknowledge things that I think may have been hard or times when she has participated in things that I think maybe she would rather not have. Simple "thank you for......"(maybe accompanying me somewhere), or "I appreciate ..............."(maybe something as simple as helping around the house)or "I really enjoyed being with you when we.......".
By checking in, I mean I try to at least every day, say something that shows my interest. I can't just say "Tell me how you are feeling with the PTSD" every day. So I try to approach it from various angles. "Can you share how you feel about....." or "you seem down, are you OK?" or "The grandkids were really a handful, was it getting to you?" Open ended questions that don't paint her into a corner. For example, I don't use the "Are you OK?" a lot when she is down because if she is not then that can make her feel she has to say yes or no as opposed to a question that gives her the opportunity to explain or share. This is not something you can force, however.
My wife has not had big blow ups but that is because she holds everything in. I know it must be painful when your wife says some things about you not supporting her but I guess I tend to look at things from all sides. At least she IS trying to share how she feels. It may come out as anger and could be communicated better if she didn't have PTSD, but she is trying to ask for you help, as I see it. Share that she needs your support.
Seems trivial for me to say, but hang in there. Try to not take it too personally if possible. For me, the sting is a little less if I can feel I understand the emotions behind it. This is very hard!
ISH