I looked at this song earlier. We have started using it at mass and the liturgists have been selecting it for gifts and communion. It is working well and has been learned quickly by the assembly.
A couple of things became obvious when playing the song a few times. For a lazy guitarist (like me) capo 3 puts the repeated bass note G to an open E and the bass note C to an open A – much easier, although it means playing a C#m at one point.
I also thought that Amanda McKenna was singing it differently to the music because she finishes on the C not the F to E in the top line of the printed music. When more than one voice is used the main vocal stays on the C and the harmony goes FtoE. This was probably always obvious to trained musicians, but I had to hear it sung by a group first to figure that out.