I heard her being interviewed on the radio this morning, and her main issue seems to be about not getting the first class upgrade because she only travels for 3 days and so doesn't have a season ticket. This is a completely separate issue in my mind to the passengers ignoring her.
She said in the interview that she did say to the people around her that she was feeling unwell and they did hear her because they had to move to let her sit down. However, I do feel she should have been a lot more assertive. It would not have been possible for the other passengers to have ignored me if I was in her position! I would have been tapping them on the shoulder, talking loudly in their ears, and so on to get my point across. I would have been roping in likely looking passengers to help me ask the nearest people sitting down to move etc.
I am also a bit puzzled because I thought most trains had priority seats these days for elderly, disabled, pregnant passengers or those carrying children. Southern certainly do on the line that I use the most. I would (and have) asked anyone sitting there to move, if they didn't fall into the categories mentioned. I became quite expert at knowing which carriages and where these seats were, and making a beeline for them. Always apart from 1 time, people automatically moved or didn't go to sit there when they saw me and my massive bump getting on the train.
The woman in question doesn't make any mention of whether she wanted to sit in the priority seats or not.
As a general rule, I always stand and offer my seat to anyone who looks like they need it more than me, or who has reasonably asked for it. I would never ignore someone who had sunk to the floor, clearly saying they were unwell.