Lol, I could imagine how it would be a hard concept to understand for some people as it's not really used in that context on a day to day basis.
BUT, when someone tells you it's miles PER HOUR and you still don't get it and somehow come up with some new logic about mile per minute youre beyond help
She was right though. It's not like that person is at the airport at 2:00 pm so obvi she thought it was gonna take 20 minutes to get there. 60 + 20 = 80 minutes to get to the destination!