Well, Saffie, in the case of a persistent little biter who is too young to understand otherwise, then yes, I could see that. Even my S2 (who is now S3) had a problem with biting once in a while when S6 would aggravate him -- and I could see giving S2 a small nip to let him see what it is like (thankfully he seems to have gotten the message through a gold old occasional swat to the behind.)
But foo's son is 11 years old. What could possibly provoke a grown adult woman to bite her pre-teen child? There are certainly other ways to punish a boy that age and to communicate dissatisfaction with his behavior. To me that speaks of immaturity and fear on the adult's part -- fear from not being able to handle the situation properly on her own. Kids (and some dogs) tend to bite out of intimidation and fear.
