That may be your understanding but it is not what the Union’s invitation says. That clearly says that the decision will be entirely Ms Marsh’s.
I personally think her argument is on a hiding to nothing because it’s doubtful whether there was any sort of contractual arrangement between her and the Union but that’s another matter.
Which verbal statement? There are allegedly signed documents.
And whose copyright are you trying to assert? The speakers don’t have copyright over the Union’s recording and they are not entitled to object to the Union recording the debate.