Honestly, that may work for her kids, but each child is different and they all respond to punishment differently. I walked into a pre-made family with a very obstanant teenager who my wife would regularly have to spank (yes, even as a teenager!) and I remember several times exchanges of yelling that would make a sailor blush (from the teenager's mouth, not my wife's). The younger daughter was not that bad, YET. She was just in training for what was yet to come.
I never came in assuming that I would ever replace their dad, although I wish I had. Even when he would blow up and show his a$$, they always feared that he would stop loving them, so they ended up worshipping him even though he is worthless as a father. This is the same man who when called to come pick up the older one who was at a party where there was drinking, shows up threatening to kick everyone's ass (instead of quietly picking her up and applauding her for doing the right thing), to the point that 3 of the people at the party jumped him at a football game the following week right in front of her. For the remainder of the year, I was her escort at football games due to the threats against her.
Now that my wife and I have had kids of our own, we are both on the same page as far as discipline. Time-outs are pretty common. Spankings are rare, but when they are called for, you know it. My third grader can count on one hand the number of times she has been spanked, the kindergartner can count them on one finger, but my 4 year old boy - I have lost count. My wife says that he's the spitting image of the oldest step-sister. This worries me. What we have going for us with him, though is that we are both VERY consistant with him. The main part of the problem with the older two. When you have one parent more interested in being their "friend" than being their parent, it makes for a rough situation all the way around.
I applaud those parents that can raise perfectly well adjusted kids without having to spank. I just know my kids and what it takes to get through to them. My kindergartner will react to just a stern voice, but my boy requires the physical route most times.