I do kayaking and some sailing. I can't believe she thought it was a good idea to go on a river, in flood, with a weir. You've got to know your route and weirs are incredibly dangerous. I know people who have bought inflatable kayaks and have drowned when they've gone over a weir.
When you are taking people out, you have a responsibility to them if you claim to be an instructor.
The fact that no route seems to have been discussed, no briefing, no next of kin contacts etc.
Lessons shouldn't need to be learned, These should be known already