Properly, you say... Until you are having fun - you are doing it right. In this case girl is struggling doing simple stuff. Let's put everybody on long stiff camber boards and start hating all flat, rocker, hybrid profiles with mellow flex and all god damn magnetraction technologies, because it's not proper boards, right?
Let's begin this from the start: board is rated 100-140 lbs, girl is on the bottom of the weight, she is also short, he skill , let's say, could be better. Learning is OK but in this sport having fun is more important.
http://www.gotceleb.com/wp-content/...ilje-Norendal:-Wallpaper---Sochi-2014--01.jpg
What does this picture is telling us? She must be doing it wrong
That rule does not apply for tall and skinny, they should go shorter, and does not apply for short and fat/muscular, who should go longer. For an average Joe that rule is pretty much correct.
I ordered 156 sabotage for 6"2 165 friend and 159 sabotage for 6"0 185 brother, I know the concept, don't worry.