well first off, i just want to mention that the amount of compassion and understanding you are showing for your girlfriend is amazing. i also struggle with anxiety and trauma so there are a few suggestions i can think of that might help her and you:
tell her how you feel/what concerns you have (or even show her this post), it might open the door for a deeper conversation as to what is holding her back or how you can improve communication
get yourself a therapist. this serves two purposes, one being so you can talk about these concerns and get professional advice, as well as address how it impacts you. the second reason is that it might inspire your girlfriend to reach out and give therapy another chance, especially if she sees it is going well for you (this might be a stretch, but its worth a try. many therapists are doing virtual meetings now, so it might be easier and less anxiety provoking since she wont have to go anywhere)
please, please do not let her be alone for much longer, i know this is what she thinks she wants, but i would bet anything that is only making her feel worse. the longer she stays isolated the less and less she will want to leave because it feels easier to stay home and never have to challenge the anxious thoughts/feelings. i understand this is easier said than done and not going to be easy by any means, but it is necessary. just take small steps and be patient with her.
if you go out together make sure to let her know that if she is anxious at any point, she can tell you, and you can leave. it might help to create code words/signals for checking in with how she is feeling, it would allow you to communicate silently without her having to approach you first. which can be especially useful in a group setting where you cant just ask her
if my advice or suggestions dont sound helpful thats totally okay, i wish you and your girlfriend the best of luck!