"Ffs, why does she keep going on about “causing offence”? What does that even mean, in practice, and why does she only seem to care about perceived offence in one direction?"
Yes, that looked strange to me also. It's political debate. People will strongly disagree. They attack each other's positions. It generates some heat, and some people are always going to be offended. If you find yourself getting angry being exposed to contrary viewpoints, you do have the option of limiting what you watch.
I think the emphasis should be on open and robust debate of the issues; not being "sensitive" because some people might get offended. Oh you're easily offended? Then stay away from political debate.