Intelligence =/= spatial awareness or cubing ability.
I taught my ex girlfriend at uni how to solve the cube using a weird beginner's method I used at the time. Took a LONG time and a LOT of patience, and the hardest thing was getting her to understand the concept of the cross. Bearing in mind she spoke 8 languages fluently, had never got a grade below an A in her life, and a few months later graduated with joint 1st class honours from Oxford. Pretty smart girl.
My favourite explanation is the concept that the cube is made up of 3 axes (plural of axis, not three axes as used by lumberjacks, that would be weird), which meet in the centre. These axes are fixed, and the other pieces rotate around them. The cross is solved by moving pieces from an incorrect axis onto the correct one, with the correct flip/orientation. In order to correct the flip/orientation, you just need to take them OFF the correct axis, turn the adjacent axis, then return them to their correct axis again.
Demonstrate the movement of the pieces AROUND the axis by doing R2/whatever2 on a solved cube. Let them play with the cube for a while.
I think it just requires persistence and patience to teach anyone to solve the cube. As the saying goes - there's no such thing as a bad teacher, only a bad student. If you get frustrated with the student then they will give up. With enough patience, you can find the method that give the 'Eureka' moment for anyone solving the cube, whether they understand it mathematically, algorithmically, spatially, or what have you.
As an example, I used the axes explanation with my brother-in-law, who's a mechanic and high-school dropout. He understood immediately and solved the cross straight away (in about a minute). He then proceeded to solve the white face (albeit completely wrongly, but one face all the same colour!) with no further guidance. I showed him his mistake and he understood.
So a mechanic with little education can 'get' the concept in minutes, while it took me weeks to get through to a girl with a genius level IQ. Go figure!
Then again, the person has to
want to learn. If she's not interested, make sure she's got a book/ipod/ejector seat, because 11 hours in the back of a car is a long time, especially when the car isn't parked, and your parents are in the front!!!