The problem was that Edwina is obviously someone who relishes a debate. Not just because she is a politician - she hasn't done anything in politics for years - but because she is a confident, opinionated person, a bit of a rent-a-gob, someone who genuinely enjoys putting a view and standing up for it. So when she heard Kendra saying something she thought was nonsensical, she sat up and expostulated.
But Kendra's background is obviously not that at all. She is someone famous for being 'herself', not for her thoughts on issues of the day. I should imagine that people who work with her are extremely deferential, as American tv tends to be to its stars. She is used to being listened to with respect and admiration. When EC sat up and contradicted something she said, she didn't think, as Melanie, say would certainly have done, "let's see if I can defend my view"; she thought - why is that NASTY woman not agreeing with me?
I find it a bit depressing that so many people are defending Kendra's part in this and seeking to put all the blame on Edwina. I am not even slightly fond of Edwina, but Kendra's foul-mouthed tantrum was not even slightly justified by anything Edwina said to her. And it will do her no harm at all to learn that silent admiration is not the only possible response to everything she says.