Read the story, and also look at her account of events on X. She makes a big deal out of saying she had not booked assistance in advance.
Of course I want disabled people to be able to just turn up and be assisted, but she is complaining that she was told that people who had booked assistance were a higher priority. Of course they are. What does she expect? For someone who has booked assistance to be left waiting and miss their train because she expects to be a higher priority?
I'll caveat this with the same caveat I added to my other comment - we only have one side of the story.
But if her description of events is correct, she was informed she was not a priority, and was eventually refused boarding because the staff member considered her rude. She is right to challenge her denial of boarding on the basis she wasn't aggressive. A second staff member was brought along who also refused boarding based on the first hand account of the first staff member.
You would think that a conversation in this scenario would go a bit like, "Sure, I'll come back to sort the ramp for you in a minute. I just need to assist another passenger first who has booked passenger assist and is waiting for us.", followed by, "Sure, no worries, I'll be here!". Something somewhere has gone awry.
I agree with the passenger than asserting their rights should not be considered rude. I also agree with them that rudeness is not a reason to refuse ramp access. It is worth bearing in mind that the passenger assist at Liverpool St is delivered by Network Rail, who are not really in the position of refusing passengers boarding based on them being rude, as that's really an issue for the train operating company to consider (who, let's be honest, wouldn't want this negative media attention and probably would've boarded the passenger).
It's probably pretty telling that Network Rail have apologised multiple times for this event. I don't want to slate the staff or anything, but it sounds like Network Rail are admitting they should've done better and even that she should've been boarded.
I will also say though that customer-facing staff do need to deal with a certain level of dissatisfaction and even rudeness from customers. I would never advocate for people being violent or aggressive towards staff, but if your job involves refusing boarding to people, you must expect passengers being rude to you. If they're being a twonk, whatever, you report them to BTP and let them deal with it. If it's a disabled passenger unable to access services because of a staff decision, then I'm afraid that dealing with the verbal consequences is part of the job. If she was effing and blinding sure, but if she's just assertively stating the law, that's part of the job. We have to remember that for disabled passengers to be denied service (whether intentionally or accidentally) can be highly distressing. We cannot be surprised if those passengers aren't friendly with us. My mum was denied service as a wheelchair user 12 years ago, and it took her 11 years to pluck up the courage to take the train again, and that was only with me as a companion. The feeling of being deserted at a station has basically left her totally unconfident in using the railway as a solo disabled passenger, and I'll be honest, I'm not sure she'll ever get that confidence back.