I didn't think about the fact that the tombstone was so old-fashioned looking, but you're right, realistically it would have been a flat stone of shiny marble.
What I did wonder about was Carolyn's name: Carolyn Collins Stoddard. Is her middle name Collins? Did Elizabeth name her that so that Collins would be part of her name? Also, the date on the tombstone was July 15. I was under the impression these episodes originally aired in June, but perhaps it was actually July. ?!?