Going down this structure isn't safe, fall off either side and you re in a closed stopper with no escape, the fish ladder wall effectively locks you the stopper.
Even if you don't, you risk being pulled back into the face of the Weir, tow back can be many meters.
She was a fucking idiot and to some extent so were the people with her, even with no training, Weirs in flood are scary places, no one in their right mind goes near them.
Paddle boards are for flat calm water.