You are perfectly entitled to sit next to other passengers.I politely told her that I could and that I couldn't see any spare seats that didn't involve sitting next to someone.
Some people are just anti-social and never have liked being around strangers. Covid just gave them an excuse to try and justify it.Indeed. Sitting diagonally opposite was also the sensible (and polite) thing to do pre Covid, especially for those of us at the taller end of the scale. It’s odd how a small minority of people seem to have forgotten how to cope with being around strangers!