Not if it's done properly. Physical discipline should be no more than a firm crack across the legs or rear. The purpose is not to hurt the child! It should also be followed by having the child verbalize what they did (even a small child who swatted their sibling can say "hit") and resolution ("I'm sorry"). I once went through a politically correct phase to see if I was wrong about physical punishment (as I just described). It was excruciating and was much more cruel than getting the child's attention by a smack. Small children do not reason. A physical smack gets their attention. It's not cruel, if it's done correctly. What this woman did was abusive. There's a difference!
If they can't out smart 'em, they out muscle 'em.