I think she means me miss pixie. Which is a bit weird, but hey some people are I suppose.
I think there is lots of ambiguity and confusion about the policies and layouts of all the different trains. I see what you mean about East Coast Trains, they do generally advise in print to fold buggies. Which is weird because half the journey I regularly do with my buggy is on East Coast, and their train staff I've generally found most sympathetic and the layout easiest. I also take the point about the assistance button, but this doesn't seem standard over all trains too.
It's this kind of confusion that makes rail travel with kids so stressful and these situations happen. The journey to my mum's involves two changes, three different train companies and it's difficult as they all have different layouts and policies. On one part of the journey there's not even a wheelchair space, just a large lugguage carriage where a wheelchair user can sit with the suitcases. I think it's as easy therefore for a person to assume that the wheelchair space and companion seat are available to buggy users if unoccupied and feel righteously angry if someone is sitting in them, as that is certainly the case and advice given sometimes. And therefore be pissed off and be considered rude. and it's also easy for a person who is sitting in the wheelchair space to assume that the buggy user should just fold her buggy and go away. Especially if she's been erroneously or otherwise allowed to book tickets. and then be a bit rude in return, tutting and the like.
So I think both parties on the train were unreasonable and reasonable at the same time through their own assumptions, but the main problem was the inconsistency and unfairness in the rail companies attitude towards people travelling with children in buggies.
If there was just some consistency and a decent policy to allow buggy users to book a space then situations like this would not happen. I am arguing with the OP not because i think she was blameless, I do think she was mouthy. But rather because I can empathise with her position, and her feeling of righteous indignation, although possibly misplace depending on the status of the seat, which we aren't going to know for sure. I also empathise with her stress levels about taking a young child on a train journey. As I've said before, just because you find taking one child on a three hour journey easy, then you shouldn't assume everyone does. You might just be blessed with a less stressful child and a more organised brain.