Your friend is humiliating her son and in so doing she is breeding anger, resentment, and revenge in him. He's made up his mind that she will not "break" him with these punishments and she may in fact be fueling more of his bad behavior, as this becomes his way of getting back at her. Unless she tries to substitute building a relationship with her son, this power struggle will continue and become worse. If there were any way that you or another adult could help her to attend some parenting courses, you would be doing a great service for their relationship and his well-being.
Washing a Child's Mouth Out with Soap
Toddler and Teenager Expert Advice from Carleton Kendrick, Ed.M., LCSW