Invasive plant lists vary by state... Although it's a European introduction, I don't think we need to be concerned about ox-eye daisies around here. A little googling and I found that it's considered invasive in several Western states, but on the East Coast and in the Midwest this statement from the Minnesota DNR seems to sum things up: "Oxeye daisy can become abundant in disturbed areas, but is not thought to be a big threat to high quality, native habitats."
Thanks, Sue. I'm looking forward to going back to the area, hoping to take some extra time there beyond the planned family weekend. Jim might have to work -- but Joyanna will be out of school!