It's never fun to be on the receiving end of criticism or, worse yet, interference, from someone, no matter how good their intentions are. Yes, that woman may have raised twelve kids, so she knows what she's talking about, but you are an expert when it comes to your child.
Maybe it has happened to you. You are minding your own business when your child acts up or wants something unacceptable, and someone--a family member or even a complete stranger--butts in and offers you some advice, encouraging you to give in to your child. Certainly they want to diffuse the situation, and end the crying/complaining/begging. But a true Mean Mommy has to stand her ground, even when being ganged up upon by her child and a third party. Especially with the third party! When a parent gives in, the child learns what to do to make the parent cave the next time. If it requires carrying on to such an extent that someone intervenes on their behalf, so be it. That's what they will do. But that third party interference can also send the message that Mommy Is Wrong. If the person in question is older or otherwise appears to have more authority, couldn't that reenforce the child's behavior, encouraging them to believe that they are being treated unfairly? Like when someone offers your child a cookie, and your child really wants it but you decline. Your child whines and pleads, but you stand your ground. The other person snorts and tries the old "One cookie won't hurt him", to which you once again refuse. Then they might have the nerve to say, "Well, I'm sorry, but your mommy said "no" ". Um, passive aggressive much? Maybe you have a good reason for saying "no". Maybe your child has dietary restrictions, or maybe he or she just ate a whole tray full of cookies and you're worried about a tummyache.
Mean Mommy K was at the pool when her 4-year-old decided to throw a tantrum. Not fun, but every mommy has experienced it. It's a rite of passage that sucks for everyone. Unfortunately, the tantrum thrower was blocking the door, which led a seemingly kindly, elderly lady to try to "help". She addressed K as "Mom" in a condescending tone then proceeded to tell her what to do. Really? Isn't a tantrum bad enough in itself? Is it really necessary to imply that a mom is handling it the wrong way? And is there one "right" way to handle a tantrum?
If you have never been caught in the middle of a child's tantrum (like, if you don't have kids), let me explain what is going on in a mom's head during one:
"OMG, please, not now. Please stop. Great. She's not &*^#$@! stopping. What am I gonna do? Crap, people are looking at me. Oh, well. It happens. She'll stop. I just have to ride it out. Kids have tantrums all the time. It's normal. I hate this! Why won't she stop?! People are staring. Really, what am I supposed to do?! Drag her out by her hair? What are you gonna do--call the Mommy Police? Fine! Keep staring! Enjoy the show! We'll be on our way when she's done. Please stop. Please, please stop. Please...Why won't she stop?..."Exactly how is offering condescending advice going to do anything but make a Mean Mommy cuss you out in her head?
As for the "helpful" lady offering her advice to Mean Mommy K? Was she really trying to be helpful? Or did she really think that K was hopeless? Or, maybe, was she passive aggressively trying to annoy K so much that she would grab her tantruming child and drag her off to carry on somewhere other than in front of the pool door...hmmm.....
In any case, the only reply I can think of that works without offending is "Thanks, but I've got this". Keep the cussing in your head.