I've been told that some cathedrals and churches in Italy frown on women wearing sandals into the church...is that true?
I have only worn sandals in all the churches that I have been in. No problems yet.
Since many monastic orders wear sandals, especially in summer, you should be okay with just about anything.
I've never seen that.
No, we've never encountered any footware rules.
And I'm pretty sure the founder of that particular religion was partial to the same kind of footwear. :-)