I think some of the more heated argument in here is coming from dueling definitions.
From a Christian POV, the term "pagan" is exclusive, it means someone who is not, never was, doesn't believe in, the judeo-christian mythos. You can't be a christian and a pagan at the same time.
But to a neopagan like myself, the term "pagan" is not exlusive, it is inclusive. "pagans" are those who believe in more than one deity/mythos at a time. So, from my POV, those Kildare nuns could have been both Christian AND pagan - practising pagan rituals when they were needed right alongside and within christian practices, without any conflict.
Now, I know what you're gonna say: The Bible forbids that kinda thing, so a "good christian" would never knowingly practise paganism. But, there's a difference between the way something is written and how it is practiced, especially among the "common folk".
To cite a non-western example: Mahayana Buddhism incorporated many local gods and beliefs into its structure when it spread east out of india. The original buddhist scriptures are now only a teensy part of a truly vast religion that varies from place to place throughout Asia. Buddhists see no problem with praying to whomever will get the job done, from saint to deity to even demons, without any conflict of interest.
Just my $.02