Yeah I figured AB.
Reason I suggested slabs Is because It's cheaper. You get 6 slabs for every 3 blocks. But only one button for every block. And it works the same. I guess it's a matter of taste, whether we want the ice to show or not.
As for the side part, If mobs can't spawn on the actual Ice path, they made might be able to spawn next to it and walk on to the ice. I'm guessing that's what she meant.