I agree with everyone, but the way this has been said would have put me on the defense too. Having someone you don't know shake a finger in your face and tell you that, essentially, you are a bad dog owner is enough to make anyone bristle.
To be honest, I think Paige put it the best...Also, we are all adults here and making comments such as "Sticking your fingers in your ears and going "LA LA LA I CAN'T HEAR YOU!" isn't helping anyone" is both unnecessary and immature (have you considered too that this may be happening on both sides).
Also, as in the horse world (this is why dressage barns don't talk to hunter barns who don't talk to jumper barns, who don't talk to western pleasure barns, who don't talk to HUS barns, who don't talk to eventer barns, etc.) everyone has their own way of doing things, and yes everyone is bound to disagree over just about anything when it comes to the training, care, nutrition, etc. of their animals. Yes when I see a 2 year old horse under saddle at the shows it ticks me off because that horse is way too young, BUT I don't march up to the owner and tell them off. If it comes up in conversation I'll ask why they're riding them so young, and provide some articles from reliable sources (think scientific journals and veterinary publications) that show why riding a horse at such a young age is not a good thing. I usually get a positive response that way...as in the person listens to my opinion and reads the material that I provided. It doesn't mean that they will change their minds, but at least I've got them thinking.
When we run in with the cavalry first thing we tend to shut our minds down, and so does the other person that the perceived attack is against. She's not doing this to personally offend anyone, so we don't need to be so offensive either. Also, as I have said earlier, she might be more receptive to learning if the approach had been different. In stead of "you're doing this wrong, in doing so you are being an irresponsible pet owner and your dogs are suffering", perhaps "wow, it seems like you have a great time with your dogs. I'm curious, can I ask why the jumps are so high?"; that, IMO, opens the door to a productive discussion of the risks associated with jumping high jumps that don't have a break-away safety feature.
again, this is just my opinion...I heard a quote once, and I'm probably going to get flamed for this, haha, but it seems to fit this situation so here goes "fighting over the internet is like competing in the special Olympics, even if you win you're still retarded", lol, and no I don't have anything against special needs people. My sister is autistic and my cousin has CP, just have a sense of humor about it, lol