Welcome to Beyond Blue and well done for reaching out.
I am sorry to hear of what you are gong through right now, with you relationship with your partner. It's wonderful that you are trying to be so supportive for her. A lot of people are not so patient and kind, nor are they tolerant. But you demonstrate that you are most certainly all those things, and that is great!
In repsonse to the questions you asked;
What should I avoid saying that may be upsetting her without knowing? You mentioned that there are some 'no go zones' but that these things also keep coming up, yeah? One of the things that I learnt (mainly by reading the book 'Men are from Mars and Women are from Venus') is that men and women have very different needs when it comes to communication. Men tend to want to help and fix and solve things ,whereas women tend to want to validate/be validated, women want to know that they are heard and that they have 'got this' without necessarily needing someone else to provide the answer or solution, but perhaps just to really HEAR what they (we) are saying. And we want empathy too. We need to know that you understand and 'get it' more than we need to know how to fix it. Why, you ask? Because knowing that you UNDERSTAND HOW WE FEEL is the very thing that helps to fix it!
How do i not take things personally and be insecure? Simply by remembering that she had a whole couple of decades or more of life before you came into it. Her thinking patterns were already well and truly established before you even exchanged glances at each other. Remember, she perhaps needs understanding and empathy, more than she needs answers, or 'fixes'.
How to help in general? Long Distance relationships are okay for a short while, but in the long term - and this is only my opinion - they become harder to maintain. Perhaps you could both consider what it would or could mean for one of you to relocate? And if relocation is not the answer or not possible, then perhaps you need to start considering what is best, and more manageable for you both in the long run? I don't know. I do know that I live 100 kilometres away from my partner, and that is plenty far enough. Consider what you can do in order to 'grow together' and hopefully, therefore enjoy each other more. Otherwise, you may just be growing apart? I don't know. I don't have all the answers.
Sorry I can't be of more help. I do hope it helps at least a little. Take care. xo