OP, how annoying and rude for you and your mother. You guys did nothing wrong and if I could go back and do anyting differently in your place, it would be to do nothing to include her in the fun once you got past sitting and chatting with her and she STILL refused to get past her snit.
I had a friend that would go on and on about California (we were living in North Carolina at the time). Everything, everyone and everyplace was just so much more sparkly, glittery and awesome in Cali (where she was from). I finally asked her when she was planning on moving back since she loved it so much. She was young enough, and unattached/not dating, so it could've been a possibility for her to do more easily than if she was married with children. In other words, it came across as an innocent question (which it only half was in all honesty). She finally toned it down about California - at least around me.
I think giving her time to get re-acclimated is fine. Then, in a kind tone - if she's still being a pill, ask if she's made any plans to go back overseas since it made her so happy.
Although, personally, I think a well-traveled person should use their experience of having been exposed to multiple cultures to make themselves MORE tolerant to be around. A well-traveled person knows firsthand that there are different ways of doing things and that 'different' doesn't mean 'wrong'. In my experience they're more open to different viewpoints and less set in their ways.
I would encourage your friend to do more traveling
so she can quit sounding like such an uppity little pill.