Perhaps I have a unique perspective on this answer because I actually agree with her sentiment. For all of you who feel like flaming or downvoting because of this, please spare me the insanity of comparing loving discipline to abuse - if you don't know the difference then you made the right choice to not spank!
Anyway, despite agreeing with her sentiment, I would never say this to a stranger like this. Part of being a parent in a free country is having the freedom to decide how you wish to instill discipline in your child. Though I may not agree with your choices, they're yours to make without public commentary (you opened yourself up to commentary in this forum, but I'm not trying to start a debate with you here).
All this assumes this woman was not directly affected by the child's behavior (i.e. they destroyed her property, etc. - more than that pesky kid is bothering her). If your child did something destructive toward her, then it is much more understandable for her to comment on your ineffective discipline (at least it was ineffective in this instance - we've all been there at some point), in addition to demanding remediation. Anyway, I'm assuming this wasn't the case based on your question.
You don't need to respond in a snarky way to try to win some argument. You know there are people who spank their kids in the world, and that fact isn't what is bothering you anyway. Don't try to address her view on that. What you need to do is address her social error - that she offered unsolicited criticism of your parenting. If this had been a private discussion with a friend, it would have been a very different matter, but the old adage of "I don't care how much you know until I know how much you care" really applies here. Given that, here are some possible responses:
- That's one approach.
- I'm sure that's what you'd do, but this is my child and I have the freedom to discipline them as I see fit.
- I'm sorry, you don't really have the standing in my life to speak to my parenting style.
- Please keep your unsolicited commentary on my parenting to yourself.
These can have different levels of "attitude", which really should be customized to the level of offense she's caused, including the attitude that she had with you. Though despite her lack of graciousness, that does not require you to omit graciousness also. Perhaps the most gracious response on your part is no response at all.