Yeah. Well, as someone whose mother would probably suffer the same, there are some people for whom video games just don't make sense.
My mum can play Wii Bowling, and Wii Tennis, but she is always slow and needs help - she'll miss the ball more often than not on the latter and always looks confused playing the former.
It's the exact same reason why I've never tried asking her to play anything any more complicated, and certainly not a traditional, joypad-controlled game. Some people just don't "get" video games, because they came after the chance came for the brain to develop the necessary synapses for the reactions, I guess.
So yes, it is quite easy to be THAT bad at Portal.