Having been the person who was uncomfortable with meeting my husband's partner for the first time a lot of it for me was because there was an expectation that we would just get along and could just jump right into a friendship. I'd never met her before and had no idea if I would like her and the way that I had agreed to meet her in the first place was changed on me. I think maybe she has some stuff to work through and chances are that it will all blow over once she gets to the bottom of why she was uncomfortable. From what you've said here, Gemini, I think this is her stuff to own and you shouldn't feel guilty about it. Deep breaths and I hope the rest of your trip other than the coffee shop incident was enjoyable.
Everything will be ok in the end. If it's not ok it's not the end.