The one HUGE fight my partner and I had was over a group outing - the three of us (a V with him as the hinge) together at a close friend's birthday party. It was our first party with no kids around, the three of us, and even after talking about it, I HAD NO IDEA how I was going to emotionally react beforehand.
I, too, was extremely sensitive to feeling like I was being judged. And it affected me more than I realized because these people were friends and damn-near-close-to-family of mine. I got a bit pissy about needing time with my partner at the event, and his knee-jerk reaction was to shut down and say that I would have a better time without him, so he should just leave.
Which said to ME, in my already emotionally flooded state of mind, that all the work that I was trying to do was being thrown out in HIS frustration, and that just shot me through the roof.
End result, the three of us are NOT welcome together at this friend's house, because of the discomfort it put a bunch of people through (and this was also their way of "protecting" me).
Luckily, it doesn't seem like your issue got THIS far.
Please understand that preparation doesn't always work. You don't know how you're going to feel in a situation until you're in it sometimes. If you're sensitive to how people are perceiving you (feeling like I'm being judged and shunned is TORTURE to me, and I will shrink back and shut down), it may be worse. And it sounded like she found this out at the moment, looked to you for help, and received a frustrated response instead that seemed to invalidate her feelings and shut her down.
My partner didn't want me to feel that way, either, but I DO, and all we can do is try to work with it. So we then had a loooooooong round of talks with him, his OSO, and my friends. I'm not sure if the things we came up with will help next time, but we're all going to be more aware that the problem is there, rather than being caught off-guard by it. If it turns out to be too much work for us, then we figure out what to do from there... I'm hoping that's not the case.
Anyway, I hope things improve for your relationship... apologies if I came across in an accusatory manner - I'm looking at this from my own experience, and while it's not as raw as it once was, it still digs up strong emotions.