I am doing a cake very close to this one for a friend's parents anniversary and they would like to have this technique for the trim around the cake, I am attempting to add the picture she gave me, Any help would be greatly appreciated . Making this cake tomorrow

I'm not sure. It may be done using a crimper and then over-piped with RI?

Definitely a crimper. You can see the marks at the corners.

They did the board the same way.

I'm way late here but for future reference, this cake was covered in fondant and the edges were done with a crimper. It is very popular in the UK, at least traditionally.