Ruskie,
In my personal philosophy, impressions and guesswork are very important. You need them to come up with hunches, that can possibly be tested. That was why I was soliciting impressions, to hone my hunches.
I'm sure, what I've said has struck you as using a dousing rod. But in my experience, it really helps. Studying the map, even the mountains and looking at very lateral names - people I wasn't directly interested in, that couldn't be connected on a tree - has helped me enormously, not once, but twice. In Ireland, you need out of the box approaches.
In one instance, my starting point was actually this same "relative." Her mother was born quite close to where one of my G grandfathers was born. My G grandparents had married in the US. They were from different parishes and I hadn't even conceived of the idea that they had known each other in Ireland. This changed all that. It changed my idea of scale and direction. It helped me find 2 of my GG grandmothers who had extremely common names, and who had almost zero clues associated with them. Me finding them so close together - associated with the same townland and knowing that they had the same surname was its own check, Because I realized that they were related, though the paper record didn't go far back enough to say how.
No one searching for just one name, or just in one line, would have ever found that. It was on nobody's tree, and I'm sure I was the first person to figure it out, and likely the only one who would have ever figured it out. Because no one else would have had the patience or the right clue.
And, it all began with this same unknown "relative", and ended with two other people who were unknown relatives to each other. My closing thought: "relative" or "cousin" should never be disregarded in Ireland. It may be a snipe hunt, but it might surprise you and turn out to be profitable, even if you can't trace it.