To address the OP's original query, if he takes his girl to a place that serves really authentic Mexican, but she thinks of Mexican as Chipotle or El Torrito, she might be very disappointed, because it won't match her expectations. Good is in the eye of the beholder, after all.
My wife and I were in Little Rock some time back. Uhm, Clinton wasn't pres yet, so I guess it was a looong time back. Anyway, asked the concierge where to get good Mexican. He gave us a place and called us a cab. The cab driver looks at us like we're crazy. "You want Mexican or Tex-Mex," he asks. Mexican, we say. "He says let me take you to the place I go for Mexican."
I wish I could remember the name of he place. It was some of the best Mexican food I've ever had. Not fancy, and everyone in the building appeared to be Mexican.
Best part was the cabbie. He said, "It's going to take you an hour in there. Don't call a cab. I'll come back for you." He knew that once we'd eaten, he'd get a hell of a tip on the return ride after steering us there. I'm pretty sure though, that the hotel concierge wouldn't have liked it as much at the tex-mex chain he recommended.
I also once drove an hour and a half from where we were staying in VA to go to a place in NC that we'd eaten at before, just because their black bean soup had been spectacular. And they didn't have it on the menu that night. Turns out, they only had it when a specific bus boy was working, because he was Mexican and he was the one who made the black bean soup. We just happened to go on his night off. The French Onion we got instead was palatable, but uninspiring.