Insight? Not really - you've sussed it out for yourself. Put away the anger and keep out of this person's way - she sounds a right despot!

It wouldn't happen in any friendship of mine simply because I wouldn't let it get that far. It's a serious mismatch between two Selves with one of them completely unwilling to compromise.

Well, you're right ego comes into it but ego is your public front. It's malleable. It adapts to the situation you're in as best as it can. Sometimes that "best" is less than optimal but you have to defend your Self, your can't just become a doormat, surrendering when you basically don't approve of something. You have to stand up for what you believe in / are.

You'll never get rid of ego (in spite of what the new ageists claim here) as it's your persona, your identity, the thing that distinguishes you from everyone and everything else. (It is possible and necessary to abandon it in advanced stages of spirituality - when you "climb" beyond Self. But if you have any self-awareness in situ your ego is at work. By any and every definition.)

This seems all about mismatching and perhaps (you don't tell us much of your story here) unwillingness to compromise. If arguments are frequent you have to ask yourself in all honesty, is this really the relationship / interaction for you.

As I see it anyway.