“it seems as if they expect at least some non-Jewish people to be buried there.I hope that anyone who’s familiar with Jewish law will set me straight if I’m wrong here.”
No, you are exactly correct. For example, my sister married a man who converted to Orthodox Judaism. He’d like his mother (who was Roman Catholic) buried by him, which is not exactly “kosher,” even if very understandable.
If I was to guess, the cemetary was supposed to be a Jewish only cemetary, and some later congregation created this “inter-faith” area, which violates all sorts of things.
From other articles, the interfaith section came into being 15 years ago after a merger with another cemetary group, but it’s unclear if one has been actually been designated. The problem with this individual seems to be that she has no connection with the Synagogue at all, nor any familial connection. Apparently she or her family thought it was a nice place to be buried and bought a plot. How that happened would seem to be the issue.