Basically she was going on about how "if everyone lived in a locally self-sustaining community, everyone would be happier and healthier and there'd be less pollution." Without backing this up with any economic or scientific basis.
What I gently pointed out is that currently everything is produced as efficiently as possible, through economies-of-scale and at locations where it is most efficiently produced via comparative advantage (and thus the "globalized" economy). If one were to depart from either the large scale production or production-where-most-efficient, production would obviously be much less efficient; meaning less would be produced; meaning there'd be more scarcity; meaning everyone can buy less and therefore everyone takes a few steps down the poverty ladder.
Additionally she kept harkening back to the "good old days" when most communities were self sufficient. I pointed out that back then there were a lot fewer people and everyone had a lot more space -- there was generally something like 240 acres available to support each person, now you're living large if your "footprint" is 15. The world simply could not support the current population living at less efficient means.
Thats when she admitted "well, in my vision there'd be fewer people." This of course made several listeners ask "how?" Then she said, and I'm pretty sure she was serious "well, I think some people need to be sterilized." I could then sit back and watch as her formerly sympathetic listeners all went "wait wha?"