Thought I'd toss in my two cents here.
OP, although my wife and I have sons, not daughters, I can understand that you were concerned about leaving your daughter with strangers at a convention when G backed out.
It seems to me that even if G's story about religious convictions was true, she could have made the choice to honor her commitment regarding the shared hotel room. She could have gone to the hotel and just stayed away from the convention and thereby honored both her promise to the others and her religious convictions.
It reminds me of a very long drive I made as a young adult. I was going out with a young woman at the time whose parents spent their summers at a mountain retreat center. I arranged to drive her from the city where we lived to the mountain retreat center to spend a week with her parents. She was going to stay with her parents and they arranged for me to stay in a guest room nearby. Well, things did not go smoothly on the drive out to the retreat center. (About halfway there I remember turning to look at my girlfriend as she nagged me for the umpteenth time and I remember thinking to myself that if I continued being her boyfriend, that's what my future would be: I'd be the target of constant nagging. Sure enough, after a day or two at the retreat center, I couldn't stand her nagging any more and I broke up with her.
Here is where I am different than G. When I broke up with my girlfriend i specifically said to her that I had made a commitment to drive her to the retreat center and back again, and I was not about to abandon her on that mountain (even if I did not want to date her any more). I said I was leaving to spend the rest of that week with relatives, but that I'd return in time to pick her up and take her back to her home city. And I did. Yes, it was awkward, and yes it meant extra driving, but I felt that it was my responsibility to honor my commitment.
G could have stayed in the hotel room without actually attending the conference to honor her commitment. She chose not to.