a stab in the dark
1. A guess or estimate with very little or no assurance as to its accuracy; a wild guess. Well, this is just a stab in the dark, but I'm going to say that the answer to the question is Countess Constance Markievicz.
2. An attempt (at something) which is not expected to succeed or has very little chance of working. It was really just a stab in the dark when I tried to fix our washing machine, but I was actually able to get it working again on my first try!