I think everyone's heard the old, "Rub his nose in it" thing before...
It's just as common as, "Feeding your dogs red meat will make them crazy.."
There are a tonne of old ways of doing things out there that are still thought to be the "right" way.
An e-mail back to her, something along the lines of:
"Thank you very much for your reply, but I prefer to use more positive methods with my dogs as I tend to see a more positive response. I'm quite sure I wouldn't appreciate getting my nosed rubbed in my waste if I accidentally went in the "for show" bathroom!

..."
Perhaps something light hearted, but at the same time informative.
I agree with others though, it's sad that someone involved with a rescue organization is using these methods, but at the same time, she has to get some credit for fostering animals without a home. While she may not be doing it the best way, I thinks he deserves some credit for doing at all.