In terms of communication techniques, I find this one does wonders. It may seem stupid or artificial at first, but we've found if you really commit to it it's very helpful. The basic steps are talking in turn, using "I" sentences, and mirroring what you heard from your partner (and making sure there is nothing more) before you respond.
Google "imago mirroring technique" to get some instructions, or go straight to the source with this recommended book:
We've used this at a critical communication point, and in my experience once you use it you'll find you listen better, and when your partner is mirroring (rephrasing) what you've said completely wrong, you get to nip the misunderstanding in the bud.
On a more personal level, I see myself in your GF, as I also tend to create distance and protect myself emotionally when change is disruptive. I can only recommend you make damn sure she wants you to give her more space before you do, as I know from experience I often want my partner to do the opposite and insist on communicating/closeness in order to feel like she still cares. I know this doesn't make much sense, and it's not very productive, but that's the nature of this "self defense" mode, for me at least.
I also find it feels like your mind is creating these "defense walls" even when you know they are not good for you, and are actually pushing you away from the person you love, but (for me) there is a feeling that "I can't help it". So maybe check with her if this emotional distance is something she chooses right now, or if it's more of an "automatic" response she's not necessarily happy with, in which case you could re-frame it as something you both want to battle, and try figuring out ways to bridge the gap together. Again, these are just my experiences, she might have a totally different attitude, but I thought it worth mentioning. GL!