Harley, I think you have nothing to be ashamed about. Please dont feel bad! You have an illness and that is why this happened. You are very brave to face your fears in that way. If anything you should be proud of yourself for giving it a try! And maybe something good will come out of it. Your fiances mom might have a better understanding of your symptoms now. And you showed that you were interested in helping out in her project. That must mean a lot to her.
I had a massive panic-attact before my brothers 40th birthday celebration ( prettty huge event, we tend to go big about these things in my family), and I just couldnt attend. I felt a bit bad about it, but at the same time I was able to recognize it as a symptom of my illness rearing its ugly head... The good thing was that it served as a wake-up call for my family, and I think they now understand better what is going on with me.