Usually at festivals here in the U.S. there are multiple stages that are setup in advance and shared. It becomes difficult to carry needed equipment such as microphones. Sure, it might make sense to carry one if it is that critical, but from what I know of Cathie I am betting there were other factors involved in her reaction.

As I said previously, I witnessed what had to be the textbook example of a "bad sound check" before a gig at a local coffeehouse. Cathie and her band did not get rude, which they would have been justified in doing based on the sound persons reaction to their issues. Not to beat this to death, but as Mick pointed out Cathie cares a great deal about the way her music sounds to the audience.   

When a person enters a contract, both parties should be liable.