What kind of aquarium is it housed in? If it is in a bowl or a jar that can be the problem. The betta has bactera growing on him and it is mostlikely has dropsy or swim bladder disease. Tell your friend to get this medican maracyn-2), ... or maybe try changing his diet to a more suitible brand of tropical fish food.
Does he look as if his tail is too heavy for him and he drags it along? If so he has swim bladder disease AKA DROPSY...

It might also be a form of constipation. Is he poopin ok?
good luck..