I'm upset with my girlfriend for not knowing how many minutes are in an hour
Why would her not knowing that upset you?
It upsets me because this is a basic fact everyone should know.
Sometimes people may surprise you with their lack of knowledge. Instead of being upset at them, try teaching them the correct information. They'll appreciate your compassion and will be thankful for your help.
But I have no idea what to teach her.
Start by teaching her the concept of time and how many minutes are in an hour.