it's insane - most of them weren't wearing wetsuits and one wasn't wearing any sort of safety device.
I do quite a bit of paddleboarding - any classes/group outings I've been on you HAVE to wear a safety vest even if you're a great swimmer and it's on, say, a fairly shallow pond in calm conditions, which is probably the safest place you can do it. They will not let you on the water without it. I don't like wearing them - I'm big boobed so with a thick vest as well it makes it much harder to get back on the board if you fall off - but in flowing water they should be non-negotiable.
you are also strongly encouraged to wear wetsuits - the times I don't are, for example, in the ocean abroad in august - not late October in Pembrokeshire! They would have been freezing if they fell in even in a less dangerous area.
even if you go to a managed location (e.g. a lake/reservoir specifically set up for watersports) you're supposed to have personal insurance if you use your own gear, and you're not even supposed to go on lots of rivers/canals without a watersports license (not entirely sure about whether the route they took was one of these).
It was just a ridiculous location for anyone to go paddleboarding in that weather, let alone people with minimal experience. Even if she didn't cancel it completely (which a lot of people would have) I honestly don't understand why she didn't agree with the other leader to do it in a safer location - she wouldn't have lost any money by doing so.