My questions to you people with good social skills: does it really help to simply stay next to my colleague, letting her do the talking while I do nothing but looking at the karen in the eye?

Simple answer: Yes.

Bonus answer: If you do even more than that, just a little, you have made a friend, for serious.

Situations like this trigger my fight or flight response.

This trigger is your personal issue. I am sure the coworker also had to deal with their own personal issues.

Both contribute nothing to your question.